Newsletter

Vegetables

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

Asparagus.

We have started to see an increase in asparagus beetle egg laying activity on spears. A treatment is recommended if 2% of the spears are infested with eggs. Since adults will also feed on the spears, a treatment is recommended if 5% of the plants are infested with adults. Sevin, Lannate, Ambush, or Pounce will provide control.

Potatoes.

Continue to check potatoes for an increase in Colorado potato beetle egg hatch. The treatment threshold is 4 small larvae per plant or 1.5 large larvae per plant. If both small and large larvae are present, these thresholds should be reduced by ½ for each. Actara, Spintor or Provado will provide good control of adults and larvae. Corn borer moth populations are still low -- generally less than one moth per night. The most recent blacklight trap catches can be found at http://www.udel.edu/IPM/traps/latestblt.html. Trap catches will be updated on the IPM website 3 times per week (Mon., Wed., and Friday) starting May 6. As of this date, no potato leafhoppers have been found in potatoes.

Watermelons.

As soon as plants are set in the field, you should begin scouting for cucumber beetles, aphids and spider mites. Since cucumber beetle populations were high at the end of last season and overwintering conditions were favorable, be sure to look for beetles, especially on field edges near overwintering sites. Foliar products can provide good cucumber beetle control; however, multiple applications of a pyrethroid or Sevin may lead to spider mite outbreaks later in the season. So be sure to scout fields and only treat if populations are causing damage. Admire or Platinum can also be applied through the drip and should provide both beetle and aphid control. There have been reports of low levels of aphids on plants in the greenhouse. If plants are ready to set out, the best option is to check plants for aphids as soon as they are set in the field. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Actara, Fulfill, Lannate and Thiodan are labeled on melons and will provide melon aphid control. These materials should be applied before aphids explode. Overwintering conditions were also favorable for spider mites so begin checking small plants for mites within a week of setting them in the field. If populations increase gradually and you find a high percentage of immature mites, Agri-mek has provided good control. However, if populations explode quickly and you are finding mostly adult mites, Capture, Danitol or Kelthane should be used. No controls should be needed until 20- 30% of the crowns are infested with 1-2 mites per leaf.

Vegetable Diseases - - Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Section 18 Granted.

For the second year EPA has granted Delaware and Maryland a section 18 emergency exemption for the use of Acrobat (dimethomorph), manufactured by BASF, to control Phytophthora blight (Phytophthora capsici) in squash (summer, winter, pumpkins), cantaloupes, watermelons, and cucumbers. The section 18 label can be found at the following address: http://www.rec.udel.edu/Update02/Updatepdf.htm

in PDF format. This product is labeled at 6.4 oz/A for a maximum of 5 applications per season and a 4 day pre-harvest interval. It is a useful tool in an overall program to manage Phytophthora blight. It must be tank mixed with another fungicide labeled for Phytophthora blight, eg., fixed copper, but not mefanoxam (Ridomil Gold 4E, UltraFlourish 2E) or metalaxyl.

Sweet Corn.

To control the flea beetles that transmit Stewart's wilt plant seed treated with Gaucho, apply Counter 20CR at planting or apply insecticides once thresholds are reached or at the spike stage of growth. Plant resistant varieties whenever possible.

Snap Beans.

To prevent Pythium damping-off apply Ridomil Gold in a band over the row at seeding or apply Ridomil PC 11G in the furrow. For added control of Rhizoctonia pre and post emergence damping-off use Maxim treated seed.

Pickling Cucumber Weed Control - Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

Strategy is a pre-mix product from UAP that combines Command 3ME and Curbit 3E. It is labeled for cucumbers, melons, pumpkins and squash. In pickling cucumbers, it can be used as a pre-emergence material, not incorporated. The two pint rate of Strategy equals 5.3 oz/A of Command and 17 oz/A of Curbit. If using Strategy for pickling cucumbers, 8 to 15 ounces of Curbit should be added to obtain the desired Curbit rate of 1.5 to 2 pints/A.

Most pickling cucumber growers have been successfully using 4-5 ounces of Command 3ME plus 1.5 to 2 pints of Curbit per acre.

Breakouts of grass can be controlled with Poast. Nutsedge can be controlled with Sandea, which received a 24c local needs label last year for cucumbers.

Field Crops

Field Crop Insects - Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa.

At this time, all spring planted fields should be sampled for leafhoppers. Within a week of first cutting, be sure to begin sampling all alfalfa fields for potato leafhopper adults. The first adults have migrated from the south and generally cause the most damage in spring planted fields. The treatment threshold is 20 per 100 sweeps in alfalfa 3 inches tall or less. In 4-6 inch tall alfalfa, the threshold increases to 50 per 100 sweeps. Ambush, Baythroid, dimethoate, Mustang, Pounce or Warrior all provide effective control.

Field Corn.

With recent rains and cooler weather, be sure to watch spike to 3-leaf stage corn for slug activity. Slugs can easily be found under the trash in no-till situations. Treatment options for slugs include the application of metaldehyde baits ( e.g.Deadline MPs and TrailsEnd LG) or the use of liquid nitrogen at the spike to one leaf stage. In general, both treatment options will help to reduce the slug activity buying time to enable the crop to outgrow the problem.

Small Grains.

In addition to grass sawflies, the first true armyworms have been found in wheat and barley in Kent and Sussex Counties. Since sawflies can quickly clip heads in both crops, early detection is critical. Be sure to shake plants to dislodge larvae feeding on the plants during the day. In both crops, the treatment threshold for sawflies is 2 per 5 foot of row innerspace or 0.4 per foot of row. The armyworm threshold is one per foot of row in barley and two per foot of row in wheat.

Black Cutworm Pheromone Trap Counts

April 20 through April 26, 2002

Trap Counts Provided by UAP Inc., Seaford, DE and University of Delaware IPM

Location	# Moths	Location	# Moths
Argos Corner	0	Lincoln	1
Bridgeville	2	Little Creek	19
Cheswold	0	Middletown	10
Dagsboro	1	Milford	0
Delmar	0	Milton	0
Georgetown	0	Sandtown	1
Greenwood	0	Seaford	0
Harrington E	1	Selbyville	0
Harrington N	3	Smyrna	2
Kenton	0	Townsend	6
Laurel	0	Wyoming	2
Lewes	0

Field Crop Diseases - - Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Wheat.

Powdery mildew is increasing since the return of the cool weather and rain. Be sure to check your fields regularly for the presence of mildew. Most wheat is headed out so the window for fungicide application is narrowing. Fungicides (Tilt or Stratego) cannot be applied after flowering (Feekes Growth state 10.5). Many varieties have some mildew in the lower part of the canopy, but none in the upper part (the flag leaf and the two leaves below). If the wheat is flowering or has flowered and there is no mildew on the top three leaves, fungicides are not necessary for powdery mildew under most conditions. Some varieties such as Roane, Pocahantas, Century II, Coker 9025, need to watched. They have heavy infection levels in the lower canopy in our Middletown variety plots and have the potential for infection in the upper leaves as well if the current weather pattern continues.