The New Agriculture Network's on-line newsletter with seasonal advice for field crop and vegetable growers interested in organic agriculture.
Vol. 2, No. 2 - May 12, 2005
In this issue
Next issue posted May 25. Read previous issues through our calendar of issues.
Planning for the 2005 soybean aphid population
David Voegtlin, Center for Ecological Entomology,
Illinois Natural History Survey; and Robert O'Neil,
Entomology,
Purdue University
With soybean planting well underway for 2005 there is a lot of concern about potential pest problems, both rust and aphids this year. Following a year in which the soybean aphid was widely distributed in the Midwest but rarely common enough to generate concern, the question is what about 2005?
There are a number of factors that come into play that determine aphid numbers. The soybean aphid survives the winter as eggs on common buckthorn (scientific name: Rhamnus cathartica), an exotic, weedy, shrub common in much of the Midwest north of I-80. In the spring these eggs hatch and several generations on buckthorn produce winged aphids that migrate in search of soybeans. For the past four years a suction trap network has been operating in Illinois. While we have been unable to monitor the spring movement of aphids from buckthorn to soybean, we have been able to monitor the fall flight of aphids from soybean to buckthorn.
In 2001 and 2003 we had low fall flights and the next growing year the soybean aphid was not a problem. In 2002 we had a large fall flight and we experienced a major and widespread outbreak of the aphid in the 2003 production season. The fall flight in 2004 was the highest yet, begging the question: "Does the large fall flight of 2004 mean that 2005 will be a repeat of 2003?"
This question is difficult to answer because many factors can influence the size of the following year's aphid population in soybeans. To start with, large numbers of multi-colored Asian lady beetles can be found on shrubs and trees in the latter part of September and into October. An abundance of these predators on buckthorn can effectively prevent the deposition of over-wintering eggs, and the subsequent production of spring migrants that fly into soybeans. Those eggs that are successfully deposited must survive the winter and after successfully hatching, they need to survive the spring weather. Heavy rains and sub-freezing temperature in early spring can eliminate young colonies on buckthorn. In the spring, lady beetles (and other predators) become active and will feed on soybean aphid colonies on buckthorn. Timing of planting can also impact the success of the spring migration. Outdoor cage tests and field observations in central Illinois have shown that many winged aphids leave buckthorn in late April and early May. This migration often precedes the planting and emergence of much of the soybean crop. (This gap between the migration of winged aphids from buckthorn and the availability of soybeans decreases in the northern growing regions and increases in the south.).
Finally, a spring migrant successfully finding soybeans does not necessarily guarantee the development of a colony. Studies by various university researchers have shown that a number of natural enemies, both predators and parasites, are present in soybean fields. When these natural enemies are eliminated or excluded in field experiments, soybean aphid colonization is more successful and population growth is rapid. So while the aphid can outbreak, the factors that lead to an outbreak are many, and all along the way lay pitfalls that prevent or ameliorate aphid outbreaks in any given year.
Spring of 2005 field observations
There have been a number of reports from throughout the Midwest of aphids on Rhamnus. Dr. Ho Jung Yoo of Purdue has been monitoring colonies in Indiana. Dr. Ron Hammond at The Ohio State University documented egg hatch around the last week of March. Dr. Christina DiFonzo from Michigan State University noted egg hatch in early April. In Illinois, we have found colonies in the Quad cities and in the Rockford area as well as in Champaign.
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A soybean aphid fundatrix (mother) and nymphs on the underside of a Rhamnus cathartica leaf. Taken on 19 April in Moline, Illinois. |
But how do we interpret these findings? It seems inevitable that there will be more aphids than in 2004, but will populations reach the pest levels seen in 2003? The best we can say now is maybe. We now have an economic threshold (250 aphids/plant), and farmers are now well aware of the damage potential of the soybean aphid. Unlike in 2003 when farmers did not realize the impact the aphids were having on their plants (thus allowing their populations to grow), it is unlikely that growers will tolerate a similar build up of aphids this year. The local control of aphids may, therefore, limit the production of large numbers of winged aphids that would fuel a widespread outbreak. However, on the flip-side, chemical control measures against populations reaching the threshold level can wipe out the local predators so that any winged aphid arriving in one of these sprayed fields will experience less resistance to successful colonization. Likewise the aphids surviving an application would have few natural enemies left to prevent aphid population build-up and the field may experience a "rebound" effect leading to faster aphid population growth and pest damage.
So what can farmers do? Farmers should know that there are lots of people looking for the aphid and they are networked. News of infestations travel fast and farmers should have good lead-time, particularly if they keep in touch with their local Extension Service, fellow farmers and state Land Grant Universities.
Second, farmers should be scouting for aphids. A weekly visit to their fields to examine even a few plants will help them keep abreast of aphid population growth in their crop. Third, farmers should use the threshold of 250 aphids per plant. To use the threshold properly, it's important to know if the aphid population is increasing and that's why farmers need to visit fields regularly to look for aphids. And fourth, farmers should not panic! Just because they have some aphids in their field does not mean they will reach the threshold of 250 aphids per plant. The natural enemies in their field are providing free pest control in most fields and in most years. Spraying fields before the threshold only helps to disrupt the control these natural enemies provide and does not guarantee economic control. The temptation to "tank-mix" a little insecticide with an herbicide (or fungicide) application "to get those aphids before they get me" is to be avoided! Looking for aphids, checking the threshold, and then deciding if you need to do something, is the key for this year's aphid pest management.
Organic production
And what about organic producers or those that just don't want to spray their crop? Well, the good news is that soybean fields, particularly those in more diversified farms or areas, have lots of natural enemies that really help in aphid control. In most fields and in most years these beneficials are sufficient to keep the aphid at bay. Unfortunately, we don't have many biological control options on the shelf, and farmers should be leery of untested methods that promise aphid control. Many researchers in the Midwest are working on finding additional options, including work being done in Asia to identify the natural enemies there that prevent the aphid from being a problem in its native home. If we can find a safe and effective natural enemy, we may be able to make the soybean aphid a pest of the past, and save farmers from having to manage this major, yet occasional pest of soybeans.
Disease migrations
Dan Egel
Botany and Plant Pathology,
Purdue University
Perhaps no plant disease in recent memory has gotten more press than Asian soybean rust. While all the publicity will help soybean growers prepare for the possible arrival of this disease, I have noticed some confusion as well. Soybean growers can expect Asian soybean rust to move in a northerly direction each season. However, not all plant diseases work in this fashion. This article will compare and contrast different methods whereby plant diseases may gain entry into a field near you.
The way plant diseases move around depends largely on how they survive the winter. Most plant diseases survive either in crop residue (residue borne), soil (soil borne) or in actively growing plant tissue (green tissue). Since Asian soybean rust has gotten so much publicity recently, let's talk about diseases that require green tissue first.
Diseases that require green tissue in order to overwinter include Asian soybean rust, cucurbit downy mildew and tobacco blue mold (cucurbits are crops in the gourd family). These diseases will only survive on growing plant hosts in the southern
Diseases that require green tissue to survive will not cause disease every year in every state. For example, cucurbit downy mildew of cucurbits does not always cause a problem for Indiana growers. Nevertheless, it is a disease for which growers must be prepared. Likewise, no one knows whether or when Asian soybean rust will arrive in Indiana or any other state this season.
Many vegetable crops are affected by forms of the powdery mildew fungus. Although this disease requires green tissue to survive, a resilient structure may be formed that overwinters. Thus, powdery mildew may survive in crop residue or may blow in from the south in the summer. Powdery mildew, as for example on pumpkins, is present in most states every year.
A number of the diseases that plague vegetable growers each year are residue borne diseases. These diseases overwinter in the leaves, stem and fruit of the crop as it decays (residue). The disease causing fungus or bacteria will not survive long once the crop is completely decayed. This is the reason that crop rotation and fall tillage are important management techniques for these diseases. Note that many of these diseases are compared in the table on page 36 of the Midwest Vegetable Production Guide (2005) <www.entm.purdue.edu/entomology/ext/targets/ID/>.
Examples of these diseases include gummy stem blight of cucurbits, early blight of tomatoes, black rot of cabbage and bacterial spot of peppers. The severity of these diseases in any particular field is related to the presence of the disease causing organism in recent years. Such diseases do not move or migrate north every year as described above. The presence or severity of these diseases in the southern
The third category of plant disease are those caused by soilborne fungi or bacteria. The organisms that cause these diseases survive for long periods even in the absence of any plant residue. Examples include Fusarium wilt of watermelon, root knot nematodes of a number of crops, Verticillium wilt of tomatoes and Phytophthora blight of peppers. These diseases are not easily controlled by crop rotation and fall tillage due to the long-term survival of the fungi or bacteria involved. Like the residue-borne diseases discussed above, soilborne diseases do not move north with the spring.
There are other methods for diseases to move around the country. Insects can spread some diseases, like those caused by viruses. Some viral diseases, like those that affect cucurbits, overwinter in growing hosts and move north in the summer. This is why cucurbit viruses are more of a problem on late season pumpkins than in earlier crops.
Finally, some diseases can be moved around on seeds. Once established in a field, they might survive in a number of different ways. Examples would be gummy stem blight and Fusarium wilt of watermelon. I'll write more on this in an article to be published in October.
Any of the above diseases may be a plague on your "house" this year. It may help to know which diseases are likely to survive the winter in your fields and which diseases you may need a map to track.
USDA Report on Organic Produce at Farmers Markets
Liz Maynard
Purdue University
Last year the Economic Research Service (ERS) of the USDA published a report about organic produce in farmers' markets.1 The report is linked on the New Ag Network library page, so I'll just mention a few of the most interesting points here, and some thoughts on their implications. The information was gathered in 2002-2003 by interviewing market managers of more than 200 markets across the
For people considering organic vegetable or fruit production, this information encourages serious consideration of marketing through farmers' markets. For people already in the business and wanting to sell more, it might inspire a look around for opportunities to supply tourists with organic produce, or for a farmers' market that doesn't have enough organic produce. For all farm marketers, the report is a good reminder that while customers may care about farming practices, they also care about the quality of the produce and how they are treated. Finally, the information about pricing suggests that it is not correct to assume that organic produce will come with a higher price tag at farmers' markets - at some markets it will, at others it won't.
The ERS periodically publishes reports on organic agriculture as well as many other subjects. The organic reports are available in the Organic Briefing Room at: www.ers.usda.gov/Briefing/Organic/
1Kremen, A. C. Greene and J. Hanson. 2004. Organic Produce, Price Premiums, and Eco-Labeling in
Deborah Cavanaugh-Grant notes there are two articles that will particularly interest organic growers in the current issue of FarmWeek, an on-line publication of Illinoi Farm Bureau. The articles related to organic production are:
1) Organic sector seeking rust control options
2) Organic explosion:Suppliers struggling to meet demand.
Editor's note: We are having technical difficulties receiving the reports from Illinois this week. Please check back Monday afternoon or later for additions.
Michigan
Southwest Michigan - Anthony Cinzori
Dry weather continued until today, Wednesday, May 11, when we got about one-half inch of much needed rain. The onions are all planted, along with the first beans and peas. We still need to lay plastic; this was delayed due to the dry weather. We have been shipping plants out of the greenhouses since the beginning of May. In the next two weeks we will plant tomatoes and peppers, along with more peas, beans, greens and squashes.
Southwest Michigan - Matt Wiley
Dry weather has been an aid on soil rotovated April 19-20. Weeds are just coming up and we will rotovate again just before planting soybeans.
We foliar sprayed speltz with fish emulsion this week. In the next two weeks, we will rotovate and plant soybeans.
Southeast Michigan - John Simmons
Warmer weather has spring/winter grains greening up nicely. The few farmers who dared to plant corn, soybeans or sunflowers in the April warm spell have yet to be rewarded with emergence. Weeds, however, are likin' this weather. Lambsquarter, pigweed, ragweed, and some annual grasses are emerging and unfolding true leaves. Quackgrass, milkweed, and Canada thistle are 6-10 inches tall. Rain in the past two weeks has been light and spotty with some areas receiving 0.7 inches, and some none at all.
Pre-planting time tillage is proceeding as soil conditions allow and weed emergence indicates.
Soil temperatures have passed 60 degrees on some of the nicer sunny days. Pastures are growing slower than usual. Most graziers are keeping the cows in the barn until the grass has more top.
I am still interested in early reports of soybean rust and soybean aphids in areas south of where soybeans are emerged.
Southeast Michigan - Rob Malcomnson
With the snow two weeks ago, almost 2 inches of water fell and tillage is just now possible. We are currently clipping pasture, weeding vegetables in the greenhouse, starting squash, melons and cucumbers in flats. I am also getting the corn planter ready.
In the next two weeks we'll plant veggies, corn and soybeans. Does anyone have a Meijer's contract for organic veggies? Prices?
Indiana
Northern Indiana - Dan Flotow
The weather the last two weeks has been dry and the last week warm. It has caused me to set up my drip irrigation system on my raised beds. This is actually a good thing because now I can water in my transplanted crops. But nobody waters as well as Mother Nature as long as she doesn't get carried away.
Currently, we are finishing up transplanting onions and leeks (should have been in two or three weeks ago). Next we will start planting sweet corn, lettuce and green beans (weekly plantings), melons, squashes, tomatoes, dry beans, edible soybeans, radishes, kohlrabi and fennel to name a few. As we get a bed planted, we will fertilize and mulch it with either grass clippings or shredded leaves. Before we plant a bed we go over the bed with the rototiller.
The next two weeks will see us continuing to plant vegetable crops as well as cut flower crops. We currently are on schedule according to our master plan, except for the onions and leeks. As long as we stay on schedule, harvesting for our CSA will take place as planned. Probably the most important thing for us is not so much staying on planting schedule as it is getting beds mulched as soon as they are ready to stay ahead of the weeds.
South Central Indiana - Dale Rhoads
Our weather conditions during the last two weeks have gone from cool with frost and good soil moisture to temperatures above 80 degrees and very dry ground. We had fruit set on all fruit trees (except no peaches this year due to winter kill on buds) and then three nights of frost . and nothing was hit. The cool conditions (under 60 degrees) during most of the bloom season made it a no stress fire blight season for apples and Asian pears.
We started the last two weeks with all our outside greens and herbs under heavy row covers. We pulled those off last week, not to go back on until fall. Field planted lettuce is up well, transplanted lettuce is growing nicely-4 inches across-again it is late for us this year due to extended cool spring. We started harvesting salad greens last week from outside plantings that were started under row covers. We will soon start harvesting kale, chard and cilantro.
We are tilling everything it seems. We had some tiller problems and got behind, but getting caught up now. We use stale seedbed planting method on lots of crops and are getting all tilled areas watered this week. We are watering heavily all outside plantings-both germinated and just planted. Our soil is very dry. We've been heavy watering with drip in a 100-foot greenhouse that has been transformed from salad greens to basil and tomatoes over the past two weeks. Tomatoes are growing well and blooming.
Everything that was under the heavy row covers is being weeded right now. The first weeding is done on outside row crops like head lettuce. We are just starting on transplanting more herbs and some cole crops. We are also staying up with fruit tree sprays. As stink bug has not shown up yet, I am not being as vigorous with keeping up with Asian pear spray, but am concentrating on apples and plums at this time when they are under heavy pest pressure.
We are doing some organic weed control trials here this year. The basic idea is testing some different herbicides. The flamer is like operating a mini jet airplane-really fries the weeds. "Burnout" appears at this time to be working a little better on both grasses and general broadleaf weeds than vinegar at 10 percent and Matran at 5 percent. Burnout even appears to work better on grasses than the flaming, but costs are not factored in there and the Burnout is a very high concentration. I think upping the amount of Matran and vinegar will produce similar results. Anyway all of this is just speculation or early observation at this point.
During the next two weeks we will be:
- Tying tomatoes in the greenhouse.
- Continue tilling to get all land germinating weeds for creating stale seedbed as rotation of planting comes along.
- Planting salad greens every week.
- Transplanting the last of our vegetables-squash, some late cole crops, etc.
- Keeping up with fruit tree sprayings-about six more weeks of heavy pest pressure for them.
- Watering-looks like it might be a hot, dry one.
This is the busiest time of the year for us and will be that way for next month or so.
Illinois
Northern Illinois - Dave Campbell
There have been no weather conditions that have affected my cropping system as it has been very dry until this morning (May 11). I am almost finished with plowing cornstalks which will be planted to soybeans. In the next two weeks I will be planting corn and equipment maintenance.
West Central Illinois - Jon Cherniss
Luckily we did not get that much rain in the past two weeks and we were able to get a lot of work done with and without jackets. Over the two week period we had several 50 degree days and 30 degree nights followed three days later with highs of 87 and lows of 50. With the dry weather we were able to mow and till our rye and vetch. The rye was over 4 feet tall and headed out. We planted our first summer crops in the field. These included tomatoes, peppers and squash. Greenhouse tomatoes are growing rapidly and we are trying to keep pace with pruning and trellising. We have also been cultivating spring crops. Our first farmers market is this Saturday. With the harvest season beginning, there is a lot of cleaning that needs to be done in our packing shed. We will also try to keep up with cultivation. Our main summer plantings don't take place until early June.
Central Illinois - Dave Bishop
Soil conditions are pretty dry, with periods of very cool temperatures (a light frost this morning) which are rather uncertain for beans and vegetables. We're ready to plant soybeans this week. Also we need to set out tomatoes, peppers and other vegetable crops. Hopefully it will warm up a bit. In the next two weeks, I will be cultivating and doing pasture rotations with livestock.
Southern Illinois - Stan Schutte
DRY DRY DRY. So far we have been OK, but it's hard not to wonder about the summer. Today (May 11) was really hot and new transplants are showing stress. I finished regular corn planting. I need to mow hay as soon as the weather clears up -- they have been forecasting rain for the last week. I planted another bunch of potatoes, sweet corn, tomatoes, and cabbage. Our asparagus is recovering from cold weather last week. Next week we will bale hay, plant regular soybeans and more produce. My first farmers market start Saturday.
