Posts Tagged ‘20:11’

Options for Postemergence Weed Control in Sweet Corn

Friday, June 1st, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Two broad-spectrum herbicides that have exhibited good crop safety to sweet corn are Impact and Laudis. Both products perform better with 0.25 to 0.5 lbs of atrazine. Both will control a broad range of weeds and grasses. It is important to consider crop rotation prior to treating sweet corn fields with a postemergence herbicide. Double-cropped vegetables are very problematic since few products allow such short rotations. Products that will allow double-cropping include Aim, Basagran, and Cadet. But these products only control small (less than 2 to 3 inches tall) plants. Most other herbicides are either not labeled for short rotations, or they have precautions about potential crop injury. Be sure to read and follow herbicide labels.

Cucurbit Downy Mildew Found in New Jersey

Friday, June 1st, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Cucumber downy mildew was confirmed in Gloucester County, NJ on May 30 and reports of CDM from North Carolina are increasing. Cucumber growers are encouraged to apply preventative fungicides immediately and scout their crop for symptoms of disease. The progress of the disease can be monitored online at North Carolina State University’s Cucurbit Downy Mildew Forecasting Center at http://cdm.ipmpipe.org/index.php.

Managing Diseases of High Tunnel Tomatoes

Friday, June 1st, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

I have received several questions about timber rot caused by Sclerotinia sclerotiorum, leaf mold caused by Fulvia fulva, and gray mold caused by Botrytis cinerea over the past week for greenhouse and high tunnel tomatoes in Maryland and Delaware.

Timber rot is common where tomatoes (or another susceptible host) have been planted in ground beds in the past. The fungus Sclerotinia sclerotiorum causes disease on hundreds of plant species. Therefore rotation is difficult. Even when a high tunnel is moved between seasons, the disease can be severe because the fungus overwinters both in and around the tunnels. Usually the primary source of inoculum is outside of a high tunnel. In the spring when the soil is moist, the fungal fruiting bodies emerge and spores (ascospores) are released. These ascospores will be released continually throughout the spring and are carried on wind into the doors or raised sides of nearby high tunnels. Ascospores are usually carried or dispersed less than 330 feet. Therefore it is important to use sanitation within 330 feet of a high tunnel. No plants, leaf clippings, potting mix, or soil from the tunnels should be discarded within this area.

There are some practices that will help reduce timber rot pressure, such as minimizing the length of time that the soil stays wet. The biocontrol, Contans has been effective in managing Sclerotinia diseases in the field. Contans, which is a formulation of the fungus Coniothyrium minitans, parasitizes the survival structures of S. sclerotiorum. If it is sprayed on the area around the high tunnel and watered into the soil, it may help reduce ascospore formation in future years. Because the product is a live organism, it must be handled carefully to preserve its effectiveness. Contans would be a good choice for fields or areas around high tunnels, which are used repeatedly for a susceptible crop. See the Contans label for additional information. Other products labeled for Sclerotinia timber rot are Endura, which is labeled for field use, and Botran, which is labeled for greenhouse use.

Leaf mold and gray mold are both favored by high humidity and therefore improving air flow can reduce the extent of disease spread. There are several fungicides that are labeled for greenhouse use that will help reduce disease. These include Scala for leaf mold, Mycostop and Decree for suppressing gray mold, mancozeb products such as Dithane F-45, and copper. In addition to timber rot, Botran has activity on gray mold.

Potassium and Nitrogen Fertilization of Fruiting Vegetables

Friday, June 1st, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Many fruiting vegetable crops are receiving additional nitrogen and potassium applications as sidedressings or as fertigation through drip irrigation systems at this time. Specific nitrogen and potassium recommendations can be found in the commercial vegetable production recommendations for Delaware which are online at http://ag.udel.edu/extension/vegprogram/publications.htm.

Balancing nitrogen and potassium properly is critical for high yields and good quality in fruiting vegetables. Growers understand the critical role of nitrogen for plant growth. Potassium is equally important for many vegetable crops such as tomatoes, cantaloupes, and watermelons which benefit from additional applications of potassium, even if soil potassium levels are high. High rates of nitrogen can be utilized by the plant and transformed into high yield only in the presence of high potassium levels.

Although potassium does not form part of the structure of vegetable plant, it is important for regulating sugar production, translocation of proteins and sugars, water balance, cell turgor, and stomatal activity. Potassium improves the quality of fruits by maintaining desirable sugar to acid ratio and improving the ripening of fruits.

The “take home” message is that nitrogen should be balanced with potassium during the cropping season with sidedressing or fertigation in fruiting vegetable crops. A 1:1 or 1:2 ratio of nitrogen to potassium should be used depending on the crop.

Vegetable Crop Insects – June 1, 2012

Friday, June 1st, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Cucumbers
As expected, cucumber beetle activity increased significantly this past week so be sure to scout for beetles as well as aphids. Fresh market cucumbers are susceptible to bacterial wilt, so treatments should be applied before beetles feed extensively on cotyledons and the first true leaves. Although pickling cucumbers have a tolerance to wilt, a treatment may still be needed for machine-harvested pickling cucumbers when 5% of plants are infested with beetles and/or plants are showing fresh feeding injury. A treatment should be applied for aphids if 10 to 20 percent of the plants are infested with aphids with 5 or more aphids per leaf.

Melons
Continue to scout all melons for aphids, cucumber beetles, and spider mites. We are finding fields with economic levels of cucumber beetles and spider mites. The threshold for mites is 20-30% infested crowns with 1-2 mites per leaf. Since beetles can continue to re-infest fields as well as hide under the plastic, be sure to check carefully for beetles as well as their feeding damage. Multiple applications are often needed to achieve effective control. Now that fields are blooming, it is important to consider pollinators when making an insecticide application (http://extension.oregonstate.edu/catalog/pdf/pnw/pnw591.pdf).

Peppers
Continue to sample for corn borers and watch carefully for egg masses. Before fruit is present these young corn borer larvae can infest stems and petioles. As soon as the first flowers can be found, be sure to consider a corn borer treatment. Depending on local corn borer trap catches, sprays should be applied on a 7 to 10-day schedule once pepper fruit is ¼ – ½ inch in diameter. Be sure to check local moth catches in your area by calling the Crop Pest Hotline (instate: 800-345-7544; out of state: 302-831-8851) or visiting our website at http://ag.udel.edu/extension/IPM/traps/latestblt.html. You should also watch for an increase in aphid populations. A treatment may be needed prior to fruit set if you find 1-2 aphids per leaf for at least 2 consecutive weeks and beneficial activity is low.

Potatoes
Continue to scout fields for Colorado potato beetle (CPB), corn borers (ECB) and leafhoppers. Adult CPB as well as the small and large larvae can now be found. A treatment should be considered for adults when you find 25 beetles per 50 plants and defoliation has reached the 10% level. Once larvae are detected, the threshold is 4 small larvae per plant or 1.5 large larvae per plant. As a general guideline, controls should be applied for leafhoppers if you find ½ to one adult per sweep and/or one nymph per every 10 leaves.

Snap Beans
Continue to sample all seedling stage fields for leafhopper and thrips activity. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. If both insects are present, the threshold for each should be reduced by 1/3. As a general guideline, once corn borer catches reach 2 per night, fresh market and processing snap beans in the bud to pin stages should be sprayed for corn borer. Sprays will be needed at the bud and pin stages on processing beans. Once pins are present on fresh market snap beans and corn borer trap catches are above 2 per night, a 7 to 10-day schedule should be maintained for corn borer control.
http://ag.udel.edu/extension/IPM/traps/latestblt.html
http://ag.udel.edu/extension/IPM/thresh/snapbeanecbthresh.html

We recently learned that succulent beans will be removed from the acephate label – this applies to all labeled formulations. At this point, we have been told that existing stocks that include the green/succulent bean usage can be sold and/or distributed under the previously approved labeling until March 14, 2013, unless EPA imposes further restrictions. We will be sure to update you as we receive more information.

Sweet Corn
Continue to sample seedling stage fields for cutworms and flea beetles. You should also sample whorl through pre-tassel stage corn for corn borers and corn earworms. A treatment should be applied if 15% of the plants are infested with larvae. We have also seen an increase in corn earworm catches, especially in pheromone traps, so be sure to watch carefully for small larvae being found in tassels. The first silk sprays will be needed for corn earworm as soon as ear shanks are visible. Be sure to check both blacklight and pheromone trap catches since the spray schedules can quickly change. Trap catches are generally updated on Tuesday and Friday mornings (http://ag.udel.edu/extension/IPM/traps/latestblt.html and http://ag.udel.edu/extension/IPM/thresh/silkspraythresh.html). You can also call the Crop Pest Hotline for the most recent trap catches (in state: 800-345-7544; out of state: 302-831-8851.)

University of Delaware Pea Twilight

Thursday, May 24th, 2012

Wednesday June 6, 2012     6:00-8:00 p.m.
Carvel Research and Education Center
16483 County Seat Highway
Georgetown, DE 19947

Tour the late pea variety trial and discuss preliminary results from the early pea trial.

Preliminary results from tillage and cover crop studies on peas will be presented.

UD Extension personnel will be on hand to answer questions.

There will be refreshments following the tour.

To register, contact Karen Adams at (302) 856-2585 ext. 540 or adams@udel.edu by Monday, June 4.

For additional program information, contact Emmalea Ernest at (302) 856-2585 ext. 587 or emmmalea@udel.edu