Looking Back at 2012 Vegetable/ Berry Pests and Diseases and Organic Management
Posted: November 18, 2012
A challenging problem new to berries this year was spotted wing drosophila. This invasive vinegar fly was introduced to California in 2008 and first seen in Pennsylvania last year. You need to be concerned because it lays its eggs in immature fruit. This means the larvae (also known as maggots) can be found in fruit that is just ripening. This is different than other fruit flies that prefer over-mature or rotting fruit. No one wants their customers to find maggots in their berries. So if you grow fall raspberries or blackberries, or even late season peaches and grapes, make sure you learn more about this insect.
Kathy Demchak from Penn State Extension has put together a lot of good information on identification and control available at < extension.psu. edu/vegetable-fruit >. In brief, from an organic standpoint you will have to work hard to keep the population low. That means harvest thoroughly. Keeping the harvest interval short and picking fruit as soon as possible has arrested the problem in some sites when the entire planting was kept clean. Remove cull fruit and destroy or bury at least two feet deep to keep the flies from multiplying in it. Managing wild berry reservoirs, trapping and exclusion are also possible options. Pyganic and Entrust are labeled for organic production (always check with your certifier) and have shown good or excellent results in field trials. Sprays targeted to kill adults and thus reduce the number of eggs and larvae in fruit should always be rotated to minimize resistance and used only if the pest is detected.
Leafhoppers, cucumber beetles, corn earworm and many early season pests were high in vegetables this year. This is not surprising since the warm spring signaled many insects to emerge earlier and mature faster. Since I saw a number of organic potato fields devastated by hopper burn this year, and short of late blight, leafhoppers are the most serious pest of potatoes, let’s review organic management options. Leafhoppers move in on air currents from the south. To predict damage potential, you can scout using sweep nets. There are a few resistant varieties to consider including Elba and King Harry, and more tolerant varieties like Green Mountain, some russets, Snowden, Ontario and Katahdin. Floating row covers can exclude hoppers early in the season. Site selection can be important. Avoid planting fields immediately downwind of barriers like hedgerows and woodlots. Barriers reduce wind velocity and increase the number of dispersing leafhoppers falling into fields. If possible, avoid planting near large acreage of alfalfa because leafhoppers move in from alfalfa after cutting. If you have mowed areas around your field, try to keep them mowed frequently so leafhopper populations do not build up and then move in when you mow. For ratings of organic pesticide efficacy and more management details, take a look at Cornell’s most recent “Production Guide for Organic Potatoes” available at < http://nysipm.cornell.edu/organic_guide/ >.
On the plant disease front, 2012 had all the normal problems from late blight to bacterial spots. Two diseases I think worthy of discussion are downy mildew in cucurbits and Phytophthora blight which primarily affects peppers and cucurbits.
Downy mildew is more of a problem recently because there are new strains of the pathogen. Dr. Beth Gugino, Penn State Vegetable Plant Pathologist, explained that, “there are a number of varieties in the seed catalogs that say they have resistance, but they aren’t effective anymore due to changes in the pathogen.” However, there are still varieties that are less susceptible such as 'Marketmore' cucumbers. Recently, new research from Virginia found that a few slicing and pickling cucumber varieties including 'Tasty Green,' 'Cobra' and 'Lider' still yielded well despite being infected with downy mildew.
“The struggle,” according to Dr. Gugino, “is there are not a lot of management options.” Like most fungi, downy mildew likes wet conditions. Try to use practices that keep the leaves dry as long as possible. That means sites with good air movement and drip versus overhead irrigation. Good weed management will also keep the air flowing and leaves drier. Keep in mind that when you use row covers you are keeping the humidity high which favors development of the fungus. Copper products (Serenade, Bacillus subtillus also rated well in efficacy trials) can help, but when it is wet and humid, conditions that favor the fungus, it is a difficult battle. In order to know if downy mildew is in your area, there is a national forecasting system that tracks the incidence of the problem as the pathogen travels up from the southern states where it can over winter. To sign up for email or text messages go to < http://cdm. ipmpipe.org/ >. We also keep folks updated via the Penn State vegetable news listserv; you can sign up at < extension.psu.edu/vegetable-fruit >.
Fruit rot in peppers, pumpkins and squash was a big problem in the northeast part of the state this year. One grower showed my colleague a field that from a distance looked as if it was recently plowed. He said, "three weeks ago that was a butternut field that was almost waist high." It was a total loss. Phytophthora capsici is hard to get rid of and can be devastating. Pay attention so you can keep it off your farm!
Phytophthora capsici infects pepper, tomato, eggplant, squash and pumpkins. The first thing you will notice is that the entire plant will wilt. You will then see the fruit get soft. You may see white growth on the fruit. It tends to be a problem in low lying or badly drained fields, but can be seen in well drained fields when there is over irrigation or excess rain.
Dr. Gugino says it was likely more of a problem this year because “flooding last fall most likely spread the pathogen between fields and farms and then heavy rains this season led to crop losses this season.” Phytophthora has special kinds of spores called zoospores that literally swim through water. The good news is that means it is unlikely to blow in from another field or other state. The bad news is it can move with water. With several inches of rain at a time, like what we experienced many times this year, there is a lot of runoff which moves the pathogen around. Phytophthora can also be spread in irrigation water especially from surface water sources that may be contaminated from run-off from an infected field. For example, one severe infestation this year had irrigation water that tested positive in two of three sites.
I asked Dr. Gugino for the top three ways to manage Phytophthora capsici. She said first, “Don’t bring it in. It can move with water or soil. If you are sharing equipment or tools be vigilant about removing soil. Infected culled fruit can also move the disease.” At one site, pepper culls with an unknown problem were disposed of in a pumpkin field near the packing shed which then infected the pumpkins. Disc infected fruit into the field already infected and don’t move it around the farm. Be careful with fruit from other farms. “One of the few management options available once you have a problem is improving soil drainage.” Use raised beds and make sure you don’t have a compaction layer. For peppers, another option is planting resistant varieties such as 'Paladin' or 'Intruder' or moderately resistant varieties such as 'Aristotle', 'Declaration', 'Revolution' and 'Vanguard'. Unfortunately, there currently aren’t any resistant cucurbit varieties. Also, scout your fields frequently and if you see infected plants or fruit, remove them and discard them on non-vegetable land to reduce potential spread of the pathogen the rest of the season. For more information, go to Organic Guides at < http://nysipm.cornell.edu/organic_guide/ >.
Here is to hoping for a great 2013. I hope this helps you prevent problems next year. Please feel free to contact me if you would like additional information on anything discussed here at email@example.com or 610-746-1970.