WEEDS, BUGS, and IPM...
an INTERVIEW with EVERETT DIETRICK
Meet Everett Dietrick,
Come up on the porch, pull up a chair, and sit with us. Let me introduce my friend Everett Dietrick, Deke for short. A lot of people call him the Grand Old Man of biological control (to his back, of course). Some of his ideas are controversial, but he came by them honestly - through years of trial, error, sweat, and observation. People respect him for the balance and wholeness of his recommendations. A fantastic range of considerations and perceptions come into play when he examines a situation.
An imposing figure of a man at 6' 5", Deke has a disarming, easy way of talking, in simple direct language. Many think that he has a PhD with his depth of knowledge, but he didnt go that route. He is knowledgeable, but not pretentious. He likes it that way, wants his ideas to stand on their merit and not be buried in showy language.
RW What is the official definition of IPM?
ED First, let's look at an EPA description of biological control: "Biological control is the regulation of pest organisms by their natural enemies, and is of major importance in pest management. The natural enemies may be native or deliberately introduced from other parts of the world. Predators and parasites of the pest species help maintain pest populations at safe levels. Frequent destruction of these natural enemies by insecticides aimed at their prey often results in resurgence of the populations of the target insect. To minimize these difficulties, the conservation of naturally occurring biological controls must become a key consideration in pest management." (US EPA Environmental Information on IPM)
RW What is your definition of IPM?
ED Now the university says that IPM means "spray" or "spray a little less", and biological control is the last thing we do. But to me, IPM is "pest management based on biological control" and should mean: "First, do everything economically possible to conserve and attract beneficial insects to the farm. Then, apply biological controls. Finally, spray if still needed, using chemicals as a last resort."
RW What is your background in IPM and biological pest control?
ED I have been practicing as an entomology and biological control consultant for about 40 years. I worked in the USDA spraying and fumigating citrus. After the war I went to Berkeley, where I became interested in biological pest control and worked in the Division of Biological Control in research. I did classical biological control for 15 years and got a pretty broad base of experience. In 1960 I went into business as a consultant with Jack Blehm, trying to enhance biological control in our clients' fields.
Through the early years we sustained our business primarily through field checking. We'd get $10-$15 an acre, which included a package of insects. That was a pretty strong support system, because we got the money first and used whatever we could to grow insects. It was really hard to determine how many insects we could grow, so we used insects from many sources. In most of my fieldwork I used field-harvested insects, taking insects from one field and using them in another. Currently I produce and market beneficial organisms with the Rincon-Vitova Insectary.
RW What role do weeds play in insect control?
ED I look on weeds as reservoirs of beneficial insects, not as problems, as long as they're not in competition with the crop. Often a grower wants to know whether to take weeds out, since we've been taught that they are a reservoir of pests. But any reservoir of pests is also a home for beneficial insects, and in the end a positive rather than a negative resource.
I have analyzed numerous untreated fields to find the best pest control practices and natural enemy complexes. Natural enemy complexes are predators, parasites and pathogens that attack pests as antagonists. I learned that the antagonists could be the most important facets of biological control. Sometimes those organisms are occupying niches, using resources, and taking the place of more harmful pests that might come into the orchard. Weeds support this community of organisms and so help with insect control.
The more you simplify an environment like a field, the more you have to do to manage it; but the more complex the environment, the less you need to interact with it. An example of extreme management is hydroponics, where all the plant's needs must be met by daily human attention; an example of minimal management is going out once a year to collect nuts in the woods. Somewhere in the middle is your growing operation. For growers, the more you let nature have a free hand the better will be the natural balance, and very rarely will there be huge increases in pest populations. Creative non-intervention sets up conditions that favor insects, birds, and mammals that keep bad bugs in check.
RW How do you farm to take advantage of this?
ED A good insect habitat needs: a "house" to live in, suitable food to eat, and some protection. Insects regulate each other by competition and food supply. They will never be a problem if you just set them against each other.
Taking weeds out because they might cause pests destroys diversity. This is wrong because the normal control complex takes care of pests. If a pest, usually controlled biologically, has no natural enemies present, its terrible; but when the pest has natural enemies, its no problem.
You can often seed beneficial insects from the insectary into a nearby weed patch before your crop comes up. Thus the weeds are up six inches before the crop is one inch, building the reservoir of beneficial insects as your plants grow. Where else can you maintain such a resource?
RW Can you give some examples of how this works?
ED The old farmer always kept weeds along the fence. In the Midwest he kept sunflowers to attract the parasites of the greenbug. Greenbug came from Europe, but became a serious pest only when farmers took away all the reservoirs of sunflower aphid, which is an alternate host of greenbug parasites, and carries the parasite when your crops aren't in the field.
Wild sunflowers are not usually looked on as weeds, unless they compete with the crops. Farmers can take them out of the field with weed killers, but they should keep them in the fencerows. Conventional weed management "wisdom", which says to take them out completely so they don't spread, leads to problems with greenbug.
Sow thistles (Sonchus spp.) carry the lettuce aphid, so they are a good summer weed for orchards. They will feed ladybugs, lacewings, and Syrphid flies, which are more summer than spring-oriented.
RW Where can weeds be grown so they don't interfere with the crop but are available to help with habitat?
ED Hedgerows are one answer. When herbicides are used on vegetation surrounding fields, we find problems with bugs because the refuge for predators has been removed. In England, where hedgerows have been an institution for centuries, their value was demonstrated dramatically when they were torn down to make larger fields for big new tractors to plow.
Then many insects which had merely been "around" became pests, because the birds that had formerly nested in the hedgerows were now too far away from the fields to gather insects. Consequently the insects didn't become baby bird food and became pests instead. Many beneficial insects and insect-eating animals also lost homes close to their supply of succulent pest insects and snails. A Society for the Preservation of Hedgerows has now sprung up to teach farmers the value of hedgerows in controlling pests.
We always look for a tolerable level of weeds. In controlling them, don't keep them in a row between orchard trees, but let them touch the trees on the side away from the sprinklers. If the leaves of the weeds touch the trunk, predatory mites which feed on plant pests can run up and down the tree and feed on the pests in the weeds, and on the pollen and nectar in the ground cover plants. If there is bare ground next to the trees, the mites will stay in the trees and feed on them instead. Some of these cover crops can also double as cash crops.
RW Do dead weeds and litter or duff have any value in weed control?
ED In almond orchards, nuts that fall on bare ground grow navel orange worms; nuts falling on duff (litter) do not, because predators in the litter eat the worms. Litter or mulch will control some pests; letting weeds grow in winter and cutting them in the spring is an easy way to provide this litter. Grapes with strict litter and weed control develop "garbage" insects - several species of Tortrix moths feeding on old grapes that weren't harvested. These moths are stored-grain pests which have become field pests because the grape growers took away all the ground (staphylinid) beetles, which normally live in the duff and eat leftover grapes. With no beetles left, the moths move in.
RW Do weeds provide habitat for creatures other than insects?
ED Don't forget the spiders. Enormous benefits come from spiders living in the litter. The long-lived ones molt and become bigger or smaller, depending on the food supply. Some insects eat spiders, but spiders eat nothing but insects and they can live for years. Of course these eight-legged friends need homes, and when the crop has been sent to market weeds can fill the bill.
RW Are there some ways of cropping that help with insect control?
ED I've seen lygus (tarnished plant bug) swarms coming out of a solidly-cut hay field - it's their favorite food. Planting strips of alfalfa every quarter mile through a cotton field will both catch the lygus bugs and provide a haven for weeds. A pure alfalfa stand isn't nearly as good for this as a weedy one, because of the enormous diversity of the weeds. For instance, if there are no onions in an area, the onion pests move to the alfalfa field and feed on a weedy relative of the onion. In fact, we feel the weedy alfalfa field sustains most of the natural enemies of the vegetable and field crops in California agriculture.
One trick we developed was cutting alfalfa hay. It is important to keep the alfalfa cut. If it goes to seed, then it attracts and grows pests. We're working with strips of alfalfa in fields of onions, carrots, broccoli, and other vegetables. Alfalfa fields should be cut in strips with alternate strips cut several weeks apart.
RW Can weeds be used as a ground cover in orchards?
ED I used to think of planting cover crops in citrus groves to replace the weeds. Birdsfoot trefoil (Lotus corniculata), a perennial legume, is a good one; hard to plant but easy to manage, and it's pretty. In Yuma some lemon trees grew near a huge spring of water. Since the soil was nothing but sand we thought we would have to grow a cover crop, but when we watered it, lo and behold a lot of plants sprang up with flowers and nectar and pollen to provide an alternate food resource for the insects. I'd much rather work with what grows locally than plant something difficult to farm. If you're busy growing lemons, why be busy with ground cover?
RW How do you encourage farmers to leave some weeds for your insects?
ED We tell people, "Why don't you save some money and skip spraying this year?" We see guys on a spray rig killing weeds, and then killing them again before they even have a chance to grow. That's crazy - an occasional weed doesn't do much harm.
I've told one farmer, "Why don't you grow me a strip of weeds every sixth row; then I'll release some insects and we'll get this IPM going?" Then I suggest, "Why don't you take your truck to the chicken ranch down the road and get some manure. Then let's put some at each sprinkler head, because if it doesn't get wet it won't be a house for a lot of beetles to live in."
RW Do you recommend composting to help control insects?
ED We find we can compost in the field. I'm a sheet composter myself; I think you should bring in the resources, no matter what they are or where you get them, and throw them on top of the ground. Basically, you're looking for cheap organic matter, preferably undigested, which will provide a home for a lot of insects and microbes. Of course soil analysis is important; you must balance the soil minerals to have healthy plants. For instance, if your soil is high in magnesium you need to add something to balance it. But composting is what you need to make farming easy for you.
I might even put a little commercial nitrogen in the mulch to make it break down faster, since something high in cellulose (fiber) and low in nitrogen (usually from protein) doesn't feed many microbes. Adding nitrogen feeds the microbes that break the mulch into humus that ultimately feeds the crop. The microbes also supply a micro food net for mites and larger bugs.
Nitrogen is nitrogen, no matter what its source. However, if all the nitrogen comes from one source, such as commercial nitrogen, pretty soon fruit tastes like ammonia and celery gets bitter. Both celery and rhubarb can soak up nitrogen until the sap has four or five times the amount considered poisonous for a water supply. They are sometimes sold on the market like that. The plant takes in water to balance the nitrogen, making it succulent but not very good for you.
RW So is feeding the microbes an important part of pest management?
ED Organic farming to me is aerobic microbes feeding on rocks. I heard a guy in England say, "Don't ever let the sun shine on the soil." If you're going to weed, leave the weeds as a duff or mulch on the surface; don't expose the soil to the sun. The sun kills a lot of microorganisms directly, and by making a barren environment it kills them dead.
If you can see the soil in a natural setting it indicates a bad situation, like erosion, poisoning, or harsh conditions. In a forest, the floor is covered everywhere with a sheet of digested or undigested organic matter in the process of decaying. Leaves are already dying and being fed on by fungi by the time they fall. Some fungi are even parasitic and feed on the leaves while they are still alive, one step ahead of the decomposers. We call them pests when they eat apples, but they're only trying to break down the apples before they get to the ground and the fungi there.
RW Are some weeds better than others for supporting beneficial insects?
ED Anything that flowers and has pollen will support beneficial insects. I particularly like plants that have aphids on them. For instance, early citrus growers planted combinations of malva (cheezeweed or mallow), vetch (vicia sp.), and white mustard (Brassica hirta Moench, B. alba Boiss, or Sinapsis alba L.). These were looked on as necessary to grow citrus when I was a kid - before World War II, when all you had to spray was cyanide. We didn't have very many citrus pests in California then.
We studied an Irvine citrus ranch that hadn't been sprayed for about 20 years to learn about biological control of red scale and purple scale.
In this combination, the malva and vetch provide a home for the general or polyphagous predators like lacewings. The malva's deep root system brings buried resources vertically from the deeper soil levels to the surface, including the phosphate the farmer's granddaddy put on the farm. The vetch fixes nitrogen to enrich the soil.
What made the combination particularly good for biological control was that the mustard in the early spring had mustard aphids, which meant a lot of parasites. Later in the summer there were green peach aphids, which also have parasites. Neither of these aphids, however, affects citrus. What citrus trees have are black citrus aphid, green citrus aphid, and others, the worst of which is green citrus aphid because its parasite, the spirea aphid, often lays eggs on other parasites. The young aphids thus kill parasites that might be effective on other aphids. Also, ladybugs don't like spirea aphid very much and don't control them well.
The gericide, or spring aphid, attacks new growth. About the time new citrus leaves unfold, the farmers would cut or knock down the cover crop of weeds with the tractor before they get too tough (especially the malva) and mix it up with the soil. Ideally, you cut the crown off about an inch below the surface of the soil. (You can reseed them when rejuvenation of the malva/vetch/mustard combination is needed - maybe every 3-5 years.) This forces the ladybugs into the trees just in time to control the aphids; the ladybugs then stay in the orchard and clean up the red spider mites. Also, in June or July when the black scale hatch, the hungry ladybugs would eat their crawlers; thus you get predator carryover from one pest to another.
RW Certain insects are usually associated with one crop. Are they considered to be domesticated?
ED You see, nearly all the insects we are involved with in agriculture have adapted their ways to man and his animals. All the pests and their natural enemies are domesticated animals just like our cattle and sheep; they have learned to live with man's imbalance and they reside on the farm.
You don't find large numbers of one kind of insect in the wild; instead, you find many kinds of insects, a few of each kind. But on the farm you do find large numbers of a few kinds of insects. And what is a pest but an intolerable level of one species?
A lot of crop insects couldn't sustain themselves without man's activities. Many of our crops, in fact, are of foreign origin and are away from their natural enemies; more and more we are going back to their home countries to import these enemies. However, we can't bring in a bug unless we can prove it will be beneficial.
RW How does antagonism help control pests?
ED Biological control covers not only predators, parasites, and pathogens but also antagonists and competitors; that is, insects that use up food and space and thus keep out plant parasites or problem insects. By occupying the space and eating the food, they occupy every niche and leave no "houses" open in which pests can live. When you spray, you take away all the natural enemies plus all the insects competing for that space, and open up their "houses" for any pest that
enters your field. In this "enemy-free space" everything becomes a pest.
In Wisconsin, organic growers complain of one or two apple pests, but conventionally raised apples have 43 pests, in niches man-made by enemy-free space, monoculture, and lack of planning.
RW Can you give some examples of how these ideas would be applied on a farm?
ED A fellow in Redding, England talks of IPPM, or "integrated predator-parasite management". Because your plants aren't natural you have to manage your environment - that is, your beneficial insect complex. Then you are no longer "farming", but "harvesting nature".
First, you look for a strain of your crop that will live without too much help. By planting all the varieties available you find the ones that will survive. For instance, there are now up to 10,000 strains of corn available, so the possibilities are extensive.
A major farm pest is corn ear worm, or corn ear worm (Heliocoverpa zea =Heliothus zea, also known as cotton boll worm, soybean podworm, and tomato fruit worm, depending on the crop under attack). Farmers who want to harvest corn sometimes plant a variety that has tight leaves around the silk at the small end of the ear, so the corn ear worm has a hard time getting in. Unfortunately this corn doesn't taste as good as other sweet corn varieties, but if planted early in the season it will withstand the pressure of early corn ear worm attack and be on the market before the other corn.
Now if you are growing cotton or tomatoes you can plant corn and sunflowers as "trap crops" to attract the corn ear worm from the cash crop. When the corn is in the whorl stage, there are two generations of Heliocoverpa per ear. In the day they are down in the whorl laying their eggs, and in the tassel stage they lay eggs in the leaves as they unfold. Any moth would rather lay its eggs in a corn stalk than on a tomato, so Trichogramma, a high-density parasite which needs a lot of host in a small area, can find the eggs easily, leaving the tomato or cotton quite pest-free. You can check the whole field just by looking at a few ears of corn, since that's where the moths will go first. Biological control kills up to 80% of them, and the birds get the rest. Later as the silk comes out you get another attack, but even though there are a hundred eggs on the silk, there will be only one worm, because the larvae eat each other in the ear. As a bonus, you can eat any surviving corn.
An old 1905 USDA bulletin from Texas recommends planting corn like this and discusses beneficial insects. It seems that everything we know about biological control was known before and forgotten, and has to be recycled for each new generation.
RW What is your strategy for using ground covers?
ED A number of plants are used as ground cover in different parts of the United States. Those that don't attract pests are not much value except as a nectar or pollen source. I prefer plants (if they're not part of your cash crop) that get eaten up by pests so you can grow ladybugs on them. The alternative is to sacrifice part of your crop to the pests and wait for their natural enemies to increase enough to protect all the plants.
In biological control you always have focal points of pest activity. To stay ahead you must recognize the first of these focal points and clean them up before the rest of them start to get dirty. The insects you grew on the ground cover now help you keep all the rest of thje plants clean. You sacrifice a corner of the field, or the first plant that get the pests, usually the first ones that come up.
This focal point becomes very important. Farmers have fumigated the soil, and starting with a sterile environment, put in fumigated strawberries or green peppers. I think even organic farmers are trying to start with a clean field. As a cultural program if you can start with a few pests, that is an advantage.
The wild gourd harbors Diabrotica (12-spotted cucumber beetle, AKA diabolica), from which Diabrotica jumps on the grower's cucumber plants. It is interesting when they come in, they actually jump on one plant more than any other.
I always thought you could go in there with a Devac (suction insect collection device) and suck them off if you had a small plot. Then the later problem would be minor. We used a leaf blower that we turned around to pull a vacuum. We replaced the original paddle blade (which won't pull a vacuum if you put a bag on it) with a curved blade that will pull.
Usually the pests get into the field first before their predators and they end up on certain plants first. A good field checker will find those first plants.
If in a sugar beet field, they irrigate the crop, it may be the first five acres watered. Sometimes you may spray the first five acres automatically instead of the whole 80 acres, because all the moths, like beet army worm, will lay their eggs on one end of a field because that's all of the sugar beets around.
That is an easy way to save a guy 95% of his spray bill just by knowing where the moths are laying their eggs. You don't want to lose the stand when it is coming up. But the insects thin it if you haven't done so yet. As you go to precision planting there isn't any room for thinning so it makes it harder to practice biological control.
RW How can a farmer use biological control on his farm?
ED It's common sense to use natural insects, it's common sense to harvest them from other sites. The university can find the ones that are effective, then it's for the farmers that benefit from them to buy them or pay for the program. And with the research being done today, better control will be easier in the future.
These methods are understandable. A person doesn't have to know the name of every insect. You can watch to see what happens and if the pest isn't increasing, you have biological control. If eggs and small larval development stages of a pest never grow beyond these early stages, this demonstrates effective biological control by
whatever combination of predators, parasites, diseases, and antagonists are present in the natural enemy complex.
How do we get the predators back? We do the reverse of what we have been taught. A farmer needs to decide how many insects he can live with. We've got to bring diversity back onto the farm, using crop rotation, interplanting, and cover crops that can tolerate large populations of insects. As you back away from pesticides, you'll find that predators come back naturally and increase in numbers. You can buy insects and augment them into your system by making periodic colonizations. An insectary can help this recovery.
But these insects need a "home away from home" and weeds in or near a field can help to provide it. So control the weeds so they don't compete with your crops, but leave enough to take care of your insect pest control.
Take a Beneficial Insect to Lunch
You too can set up a beneficial insect refuge and feeding station on some eroded or sub optimal land or unused corner in your spare time. Many of these bugs need an extra meal now and then to keep up their strength when they aren't munching on your pest insects.
Unused corners that are too wet, rocky, or steep to farm can be put to work as feeding stations for beneficials. Fence rows can be supplemented with plants that will help with pest control for your crops.
During their adult life many predators and parasites feed on pollen and nectar from flowers. This helps them live longer and have many healthy offspring. These offspring then continue their pest-eating heritage.
The way nature works is that the predators reproduce slower than their prey. This balance ensures that the young predators have something to eat. Helping some predators through the times when there is no crop in your field gives them a chance to stay in balance with the pests.
Research has shown that having pollen and nectar producing flowers in a field greatly improves pest control. We now have some ideas of the importance of insectary plants, some plants that help certain predators, and what predators eat which pests.
It may take years to perfect a scientific approach to enhancing biological pest control. The prospects for eventual success and the value of a system look very promising, based on the excellent preliminary work done.
The state of the art is fairly primitive but information is included here because the approach is very important and to promote more experiments in the area.
A lot of observations of plants with pollen and nectar available to honey bees have been published. This work on honey plants may aid the studies of others and make some short cuts possible. So some honey plant information is included here and noted for individual weeds in the reference section.
Bob Bugg an entomologist, has worked on censusing insects found feeding on flowering plants in California. His comments on some select plants illustrate some of the interactions of interest to those who study plant-insect interactions.
Wild buckwheat species (Eriogonum spp., buckwheat family)
These native California plants are drought tolerant and produce large amounts of nectar during summer and fall, attracting many beneficial insects such as parasitic flies (tachinids), Flower flies (syrphids), minute pirate bugs (anthocorids), and various parasitic and predatory wasps (sphecids).
Kate Burroughs organized a list of good candidate plants for encouraging beneficial insects (published in The Future is Abundant)
Spergula arvensis or corn spurry is a low growing naturalized weed, which often occurs in crop fields. Its flowers produce nectar which attracts beneficial insects, the most important of which are flies of the family Syrphidae and parasitic wasps. Leslie Linn, as a research assistant at UC Santa Cruz studied this plant for use in Brussels sprouts.
Since Santa Cruz County grows over 70% of the nation's Brussels sprouts, they are a very important crop in the county. One of the primary limiting factors in successful production of Brussels sprouts is pest control, and pesticides constitute a large percentage of the farmer's required inputs. The predominant pest of Brussels sprouts is aphids of the species Brevicoryne brassica and Myzus persicae.
Syrphid fly larvae are voracious feeders on aphids, the major pest of Brussels sprouts. Spergula interplanted with cabbage and Brussels sprouts resulted in crops with less pest damage than those same crops without Spergula. Spergula planted in a yard wide strip along the upwind edges of a field lead to 20% parasitization of the aphids on the Brussels sprouts.
Several researchers have been very happy with Spergula. It is non-invasive and easy to keep control of. There are other plants that might be able to attract more positive or beneficial insects but present other problems. Some questions to ask about candidate insectary plants are do they have thorns, are they hard to grow, are the seeds expensive, are they tall, do they take a lot of sun, do they take much water. The Spergula seeds were just thrown on the ground and they keep coming up and flowering all through the summer, they took care of themselves. This is a pleasant plant to work with.
Aphids will move from a host plant to the immediate surroundings but they don't cue in on particular plants, or fly upwind, just with the wind. Cabbage aphids prefer members of the cabbage family but other than that there hasn't been much work in the area. Other people at UCSC have done work on the effect of wild members of the cabbage family, or brassicatious weeds, on the populations of aphids.
As far as pests being harbored by the Spergula are concerned, occasionally Linn found imported cabbageworm butterflies. She didn't see them gathering nectar and didn't think it was a preferred or significant food source for them and didn't find any difference in the sampling. She them much more frequently on the brassicacious weeds. Cabbage (miner) can be found on mustards. You are providing a tantalizing nectar source that the adults of pests as well as the adults of beneficial insects can use. But that didn't prove to be a significant pest reservoir in this study.