Vegetables

 

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

Cucumbers.
Continue to scout for cucumber beetles and aphids. We are starting to see an increase in aphid populations. In fresh market cucumbers, treatments should be applied before beetles feed extensively on cotyledons and first true leaves. In pickling cucumbers, a treatment may be needed if you find 2 or more beetles per plant and significant damage can be found on the cotyledons. 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.  Fulfill, Thionex or Lannate will provide aphid control. Be sure to watch for bees foraging in the area and avoid insecticide applications on blooming crops.  A pyrethroid, Lannate, Sevin or Thionex are labeled for cucumber beetle control in cucumbers.
 

Melons.
Continue to scout all melons for aphids, cucumber beetles, and spider mites. We continue to see an increase in the number of fields with spider mite infestations. If populations are high at the time of treatment, 2 sprays spaced 5 days apart may be needed. The threshold for mites is 20-30 percent infested crowns with 1-2 mites per leaf. Acramite (ground application only), Capture, Danitol, Agri-Mek or Kelthane will provide control, but should be rotated to avoid the development of resistance. We have also seen an increase in aphid activity. For treatments to be effective, it should be sprayed before you see significant leaf curling. The treatment threshold for aphids is 20 percent infested plants with at least 5 aphids per leaf.  We can still find cucumber beetles, especially under the plastic. Be sure to watch for bees foraging in the area and avoid insecticide applications on blooming crops. 
 

Peppers.
In areas where corn borer trap catches are above 2 per night and pepper fruit is ½ inch in size or larger, fields should be sprayed on a 7-10 day schedule for corn borer control.  You will also need to consider a treatment for pepper maggot. If Orthene is used, it will also provide pepper maggot control. Otherwise, dimethoate should be added to the mix.

Potatoes.
Continue to scout fields on a weekly basis for Colorado potato beetle (CPB) adults and larvae. The larval threshold is 4 small larvae per plant or 1.5 large larvae per plant. The threshold for each should be reduced by 1/3 to 1/2 if all stages of larvae are present.  Avaunt + PBO, Actara, cryolite, Spintor or Provado will provide control. We are also starting to see the emergence of summer adults. Unfortunately, most of our labeled products are most effective on larvae. The higher labeled rates of Spintor and cryolite have provided some level of adult suppression; however, may not be adequate under high population pressure. Actara, Leverage and Provado provide adult control, but should not be used where Admire, Platinum or Gaucho were used at planting to avoid development of resistance.  Economic levels of potato leafhopper adults and nymphs can still be found in many fields. As a general guideline, controls should be applied if you find ½ to one adult per sweep and/or one nymph per every 10 leaves. Dimethoate, a  pyrethroid, Actara or Provado will provide control. At this point, no aphids have been detected in potato fields.

New Insecticide Labeled for Potatoes.

We now have a new insecticide labeled  for Colorado potato beetle control from Crompton called Rimon 0.83 EC.  It has a federal label; however, we are still waiting on the state label so it can not be used in Delaware until we have the state label. The active ingredient is novaluron, an insect growth regulator that interferes with chitin development and  produces a weak or malformed insect exoskeleton. Larvae are unable to successfully molt to the next immature stage after ingestion or contact with residues. Because Rimon affects immatures at molting, control will be slower than exhibited by conventional insecticides. It should be applied at the first sign of pest infestation. Rimon will not directly affect adult insects. You can tell it is working by an absence of larvae 4-5 days after application.  It is labeled at 9-12 oz/acre – the higher rate should be used on large larvae. An application should be made when egg masses are hatching within a generation. You are allowed up to two (2) applications per season against the same generation of potato beetle. Do not use it on successive generations of CPB and do not use more than 2 applications per season.  There is also an aerial application restricition: Apply in a minimum of 5 gallons/A with a 150 foot buffer zone from bodies of water; all applications must include a 25 ft. vegetative buffer strip within the buffer zone to decrease runoff.

 

Snap Beans.

All fields should be scouted for leafhopper and thrips activity, especially seedling stage beans. 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. Dimethoate, Lannate, Asana, Capture, or Warrior will provide control of both insect pests. 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. Acephate should be used at the bud and pin stages on processing beans. Once pins are present on fresh market snap beans and trap catches are above 2 per night, a 7-10 day schedule should be maintained for corn borer control.  Lannate, Asana, Capture, Warrior or Mustang are labeled.  Acephate has a 14-day wait until harvest. Since this can change quickly, be sure to check our website for the most recent trap catches and information on how to use this information to make a treatment decision in processing snap beans  (http://www.udel.edu/IPM/traps/latestblt.html and

http://www.udel.edu/IPM/thresh/snapbeanecbthresh.html). 

 Sweet Corn.
All silking sweet corn should be sprayed on a 5- 6 day schedule. Be sure to check our website for the most recent trap catches and information on how to use this information to make a treatment decision in silking sweet corn (http://www.udel.edu/IPM/traps/latestblt.html and http://www.udel.edu/IPM/thresh/silkspraythresh.html).

 

 

 

Watermelon Fruit Set Quite Variable – Derby Walker, Sussex County Extension Ag Agent, derby@udel.edu

 

Watermelon fruit set is quite variable as it is most years.  Some fields have a good set of crown fruit, others have no crown fruit. Pollination only takes place in the morning (early) and the blossoms are only open one day. You need six to eight bee visits to the flower to carry the 1,000 pollen grains necessary for normal fruit development.  To make it a little more complicated, their must be enough pollen placed on the three sections of the stigma to have a normal shape.

 

You need enough bees or pollinating insects to carry the pollen. The bees have to work the flowers on the day they are open. Some days are not suitable for flying. Bees need to see the ground to find their away around.  They don’t fly in rainy weather or very cloudy weather. They have a minimum and maximum temperature for flying (60° to 85°F). They will not fly in very windy conditions. The better the flying conditions and more food that bees need, the more they are willing to travel far from the hive.

         

This year we had some very cold night temperatures which could cause young fruit to abort. Some chemicals can cause pollination problems by damaging the pollen or ovaries. We weaken colonies by spraying insecticides. It is harder to have good pollination in large blocks, because bees may not uniformly work the field. Poor flying weather when your crown fruit blossoms are open will prevent adequate movement of pollen from male flowers to females. From the crown fruit location on the runner, female flowers (those with tiny melons) occur about every 7 to 8 nodes on the runner.

 

 

 

Vegetable Crop Diseases - Bob Mulrooney, Extension Plant Pathologist, University of Delaware, bobmul@udel.edu

 

 

Potato Disease Advisory.

 

Disease Severity Value (DSV) Accumulation as of June 17, 2004 is as follows:

Location: Joe Jackewicz Farm, Magnolia, DE. Greenrow: April 25, 2004

 

Date	Daily DSV	Total DSV	Spray Recommendation
4/25- 5/18	4	18	7-day
5/19	4	22	7-day
5/20	2	24	7-day
5/21	2	26	7-day
5/25	5	31	7-day
5/27	3	34	7-day
5/30	8	42	7-day
5/31	1	43	7-day
6/1	1	44	7-day
6/4	17	61	5-day
6/7	2	63	5-day
6/8	1	64	5-day
6/10-6/13	9	73	7-day
6/14-6/15	3	76	7-day
6/17	3	79	7-day

 

 

 

 

 

Field Crops

 

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

 

Alfalfa.

Continue to sample all fields on a weekly basis for leafhopper adults and nymphs. The treatment thresholds are 20 per 100 sweeps on alfalfa 3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100 per 100 sweeps in 7-11 inch tall alfalfa. If economic levels are present, early cutting may be the best option for control. However, be sure to check fields within a week of cutting for leafhoppers that can quickly damage small plants.

 

Field Corn.

We continue to get reports of cereal leaf beetle adults feeding on corn. In most cases, feeding is confined to field edges; however, it may also be seen throughout the field. No controls are needed unless you find 10 beetles per plant throughout the field and 50 percent of the plants are damaged.

Soybeans.
Grasshopper and bean leaf beetle feeding continues to be found in seedling stage soybean fields. A treatment for bean leaf beetle will be needed from plant emergence to the second trifoliate when you find 2 beetles per ft. row and a 25 percent stand reduction. A pyrethroid, dimethoate or Lorsban will provide control. The treatment threshold for grasshoppers is 1 per sweep and 30 percent defoliation. Asana, Furadan, Lorsban, or Warrior will provide grasshopper control. We are also seeing an increase in thrips and leafhopper activity. No control will be needed for thrips until you find 8 per leaflet and plant growth is being held back. The treatment threshold for leafhoppers is 4 per sweep in drought stressed fields and 8 per sweep in non-stressed fields. Dimethoate or a pyrethroid will provide control of both insects.

There have been reports of economic levels of spider mites in seedling stage soybeans in Sussex County, DE and Dorchester County, MD. In most cases, they are in no-till fields where mites overwinter in weed hosts. Look for the white stippling at the base of the leaves, which indicates the presence of mites. Treatment will be needed when you find 20-30 mites per leaflet or 10 percent of plants with 1/3 or more leaf area damaged. At this point, the only materials available for mite control in soybeans are dimethoate and Lorsban. We are gathering data on a new product and plan to submit a Section 18 if the data looks good – we will keep you posted.

 

 

Grain Marketing Highlights - Carl German, Extension Crops Marketing Specialist; clgerman@udel.edu

 

General Comments.

"Rain Makes Grain" vs. "Flood Makes Mud" is the mantra in the commodity markets this week, depending upon whether one is bullish or bearish. It would appear that the bears are winning at the present time taking corn and soybean prices down on the idea that the rain is generally good for crop development. What is not being asked by commodity traders just yet is whether we are making a 10.4 billion bushel corn crop, or one that might be smaller or even possibly larger. Therein lies the reasoning behind the 'bear' and 'bull' arguments in these markets at the present time. It may well be the primary question on every trader's mind, "What size are the '04 U.S. corn and soybean crops likely to be?" Perhaps a clue as to what we might expect will be given in the June 30th Acreage and Stocks reports, followed by the July 12th Supply/Demand and Crop Production estimates. 

 

U.S. corn and soybean conditions improved last week, with corn now at 70% in the good to excellent category and soybeans at 68%. Corn ratings improved 2 points and soybean ratings improved 3 points from the previous week.