Volume 7, Issue 11                                                                                             June 11, 1999


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

Cucumbers.

Both pickles and slicers should be watched for increases in aphid and cucumber beetle populations. Fresh market cucumbers are very susceptible to bacterial wilt vectored by cucumber beetles. Although pickling cucumbers grown in high-density rows can compensate for about a 10 percent stand loss, beetle feeding can reduce plant growth. If moderate feeding can be found on the cotyledons and first true leaves and there is a history of bacterial wilt on your farm, a cucumber beetle spray should be applied. Thiodan, a pyrethroid or Lannate will provide control. A treatment should be applied for aphids if 10 to 20 percent of the plants are infested with aphids.

Melons.

Threshold levels of spider mites (10-15 percent infested crowns) can still be found in watermelon fields. Kelthane or Agri-Mek are the insecticides available for mite control in melons. Chemical selection should be based on control success in the past as well as population levels. If you have not had success with Kelthane then Agri-Mek should be used first. In addition to mites, cucumber beetle levels are higher than normal. Check for beetles on 5 plants in 5-10 locations in a field as well as under the plastic and in cracks in the ground around the base of plants. A treatment should be applied on watermelons if you find 2 beetles per plant. Since cantaloupes are very susceptible to bacterial wilt, a spray should be applied if you observe moderate feeding on the cotyledons and first true leaves. Thiodan, a pyrethroid or Lannate will provide control.

Snap Beans.

Continue to watch seedling snap beans for economic levels of thrips and leafhoppers. Processing snap beans that are in the bud to bloom stage should receive an Orthene treatment for corn borer control. If corn borer catches are in the 2 to 5 per night range, a second treatment of Orthene will be needed on processing beans at the pin stage. Once corn borer trap catches reach 2 to 5 per night in your area, fresh market snap beans should be sprayed at the pin stage with Lannate. If corn borer catches remain above 5 per night, sprays should be applied on a 7-day schedule until harvest.

Peppers.

In areas where corn borer catches are above 2- 3 per night and fruit is -inch in size, peppers should be sprayed on a 7 – 10 day schedule. If Orthene is used, a 10-day schedule will be adequate and it will also provide pepper maggot control. If a pyrethroid or Lannate is used, sprays should be applied on a 7-day schedule and dimethoate should be added to the mix for pepper maggot control.

Potatoes.

Low levels of aphids can now be found in fields were Admire was not used at planting. Begin sampling lower leaves for the presence of green peach aphids. During bloom, the treatment threshold is 4 per leaf. This threshold increases to 10 per leaf at 2 weeks from harvest. If melon aphid is the predominant species, these thresholds should be reduced by one-half. If green peach aphid is the predominant species, Provado or Monitor will provide control. Lannate or Provado will provide melon aphid control. We are also starting to see low levels of egg laying and small larvae where Admire was used at planting. Provado should not be used in these fields to prevent the development of resistance. Spintor, Agri-Mek or Kryocide/Cryolite should be used. The treatment threshold for Colorado potato beetle is 4 small larvae per plant or 1.5 large larvae per plant. If both small and large larvae are present, the threshold should be reduced by for each insect pest.

Sweet Corn.

Continue to sample for European corn borer in pre-tassel and tassel stage corn. Once larvae begin to bore into the midribs you will not get control. Corn earworm larvae can also be found in pre-tassel and tassel stage fields. Fresh market silking sweet corn should be sprayed on a 5-day schedule in the Bridgeville, Dover, Greenwood, Little Creek, Middletown and Milford areas. In the Harrington, Laurel, Rising Sun, Seaford and Wyoming area, sprays are needed on a 3-4 day schedule. Be sure to check the Crop Pest Hotline on Tuesday and Friday for the most recent BLT catches (1-800-345-7544 – in-state; 1-302– 831– 8851 – out of state; www.udel.edu/IPM). v


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

Disease activity continues to be very low due to the dry weather.

Air pollution may show up on susceptible crops such as icebox watermelons or sensitive varieties of white potatoes such as ‘Norland’ as a result of poor air quality Monday and Tuesday. Ozone damage usually produces dark flecking on the upper leaf surface on the older leaves. More damage can be experienced if the crop is being irrigated, because the leaf pores (stomates) are open which allows the ozone into the leaves, as opposed to being closed when moisture is limited or non-existent.

LATE BLIGHT REPORT

DSV accumulations as of June 9, 1999 are as follows:

Location/

Emergence Date

DSV’s

June

9

DSV’s

June

6

Recommendation

P-Day

Value

Baldwin – 4/19

33

33

10-day, low rate

362

Jackewicz – 4/30

35

35

10-day, low rate

311

Art Wicks – 4/26

35

35

10-day, low rate

330

Ken/Chris Wicks – 5/3

32

32

10-day, low rate

294

Conditions continue to be unfavorable for late blight. We have yet to accumulate 18 DSV’s for potatoes that emerged after the wet period of May 5-7. v


Vegetable Diseases - Kate Everts, Extension Vegetable Pathologist, University of Delaware and University of Maryland; everts@udel.edu and Phil Shields University of Maryland; ps136@umail.umd.edu

Cucurbits

The label for Quadris was expanded this past winter to include control of foliar fungal diseases of cucurbits . In our trials Quadris used at the 15.4 oz./A rate has performed very well on gummy stem blight on watermelons as well as on powdery mildew on muskmelon and pumpkins. Quadris may be applied at a rate of 11 to 15.4 oz./A and has a 1 day PHI. To reduce the chance of buildup of resistance to Quadris in the fungal populations, alternate Quadris with a fungicide that has a different mode of action. Do not apply more than six applications of Quadris per year. It is important not to apply Quadris to cucurbits below the label rate. When possible use cultivars with tolerance to disease.

MELCAST for Fungicide Application on Watermelons.

Do not use MELCAST if there is a disease outbreak in your field, it is a preventative program. Below are the EFI values from weather stations located on the Eastern Shore June 2-9. Any questions please call Phil Shields at (410) 742-8788 or e-mail: ps136@umail.umd.edu

EFI Values for 1999

Location

6/2

6/3

6/4

6/5

6/6

6/7

6/8

6/9

U of M, LESREC
Salisbury,MD

0

0

0

1

0

1

2

3

Wootten Farms, Galestown,MD

3

3

1

0

0

4

4

4

Mark Collins,
Laurel, DE

0

0

0

0

0

2

1

2

Vincent Farms Laurel, DE

0

0

0

0

1

2

0

2

D C Farms,
Bridgeville, DE

1

0

0

0

0

1

1

2

Balvin Brinsfield,
Vienna, MD

0

0

0

0

0

2

1

2

Charles Wright,
Mardela Springs, MD

0

0

0

0

0

2

1

2

DE U of D, REC Georgetown, DE

0

0

0

0

0

0

0

--

Watermelon Fields should be sprayed with a fungicide when 30 EFI values have been accumulated by the weather station nearest your fields. Add 2 points for every overhead irrigation. After a fungicide spray, reset your counter to 0 and start over. If a spray has NOT been applied in 14 days, apply a fungicide and reset the counter to zero. The first and last day above can be partial days so use the larger EFI value of this report and other reports for any specific day. v


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

Soybeans.
At this time, grasshoppers continue to be the predominant insect pest in soybeans. For grasshoppers, treatment of non-crop areas may help to prevent whole field infestations at a later date. As a general guideline, non-crop areas should be treated if you find 20 or more grasshoppers per square yard. Remember, before bloom no in-field insect controls should be needed unless you find 30% defoliation and one grasshopper per sweep. Asana, Sevin, or Warrior have provided the most consistent control in recent years. Economic levels of thrips and leafhoppers can be found on seedling soybeans. A treatment will be needed if you find 8 thrips per leaflet or 8 leafhoppers per sweep. If both insect pests are present, the threshold of each insect should be reduced by one-third. A pyrethroid or dimethoate will provide effective control of both insects. v


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

Soybean Futures Gain on Technically Inspired Buying
Wednesday's trading session in the soybean pits was driven by technically inspired buying. Market jargon suggests that this was brought on by position squaring ahead of Friday's USDA June Crop Report and a gap on the open that passed resistance for Nov '99 beans at $ 4.80 per bushel. For the moment, traders appear to be willing to put a weather premium into the market, which is likely to quickly fade once temperatures cool and it rains in the corn belt.

Closing Remarks
Patience remains the key to marketing this year's corn, soybean, and wheat crops. The 1999 U.S. corn and soybean crops are in the ground, and for the most part are likely to be 'knee high by the fourth of July' or better. Therefore, our attention remains focused on potential weather sparked rallies, which may or may not happen. Normal or better U.S. production will result in commodity prices heading even further south than their current levels. Those with internet access can request an analysis of the June crop report by sending a message to: clgerman@udel.edu v


Control With Burndown Not EffectiveMark VanGessel, Extension Weed Specialist; mjv@udel.edu

I have seen a few fields of soybeans following small grains where the burndown herbicide was not effective for controlling marestail. [Note: these are irrigated fields]. The soybeans are unifoliate to first trifoliate stage. The cases I am aware of, used Roundup Ready soybeans. The best option is to spray Roundup Ultra at 1 qt/A and tank-mix a residual herbicide. The most consistent herbicide in UD trials has been FirstRate. Pursuit can cause greater injury and is not as effective on morningglory or ragweed. Classic can also cause injury (unless the soybeans have the STS trait) and it too is not as good on ragweed and morningglory. Furthermore, FirstRate will provide better grass suppression than Classic. However, FirstRate does not have as long of soil residual as Classic or Pursuit. If you use Roundup Ultra alone, a second application will probably be needed.

Synchrony would be the choice with STS soybeans and then the Classic in that combination will provide residual broadleaf weed control. Options for conventional soybeans are not as effective. Basagran at 1 qt/A plus crop oil concentrate is first choice followed by Classic 0.75 oz/A plus crop oil concentrate. This higher rate of Classic is likely to cause some stunting of the beans. v


Touchdown Labeled for Use Over the Top of Glyphosate-Tolerant Soybeans - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Touchdown 5 has been approved by the EPA for use on all variety of glyphosate-tolerant soybeans (or Roundup Ready Soybeans). Use rate of Touchdown is 1.6 pts./A. No surfactant is required with Touchdown 5. Touchdown is similar in activity as Roundup and expect very similar results between the two products. Touchdown is labeled for use in combination with Basagran, Classic, Flexstar, Fusion, Pinnacle, Pursuit, Reflex, Scepter, or Synchrony. v


Drought-stress Weeds - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Herbicides labeled for use with nitrogen fertilizer and ammonium sulfate can increase the effectiveness of herbicides by increasing the plant absorption of herbicides through leaves. However, this also increases the uptake of herbicide by the crop, which can lead to increased injury. So expect higher level of crop injury if you include these products. In cases of large weeds and limited soil moisture, the crop injury may be justified in return for improved weed control. The addition of nitrogen fertilizer and ammonium sulfate will help but, will not be as effective as maintaining the herbicide rates. v


Nitrogen Fertilization and Drought Stress - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

Severe drought conditions persist across much of Delmarva. At this time, it is appropriate to point out that, for dryland crops and especially corn and grain sorghum, the addition of extra nitrogen fertilizer can worsen the effect of drought and reduce yields.

For dryland corn, too much nitrogen can be avoided by adjusting your yield goal at sidedress time to account for the drought stress the corn has experienced. Also, you can use a PSNT (Presidedress Nitrogen Test) to estimate the amount of nitrogen available to the crop from organic material in the soil (manures, previous legume crops, soil organic matter, and crop residues). With this information (an adjusted yield goal and an estimate of soil nitrate availability), you can decide if there is adequate nitrogen available for the crop and avoid the temptation to add insurance nitrogen. The insurance nitrogen will not only add to the crop’s variable cost but can adversely affect how the crop tolerates the current drought stress.

For grain sorghum following soybeans, additional nitrogen seldom increases yields above the cost of the nitrogen and in some of our studies has actually caused significant yield reductions under severe drought conditions. Yields of sorghum receiving any nitrogen were decreased by up to 50 percent because of the additional stress the nitrogen caused. For grain sorghum following sorghum or another non-legume crop, the amount of nitrogen required varied from none to about 50 lbs N/A. The yield-limiting factor for dryland crops is water in most cases and not nitrogen. Keep your cost down and help reduce nutrient loss to the environment by choosing an appropriate nitrogen fertilization rate.


To Plant Or Not To Plant, That Is The Question - Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

Derby Walker, Jr. Extension Educator, Sussex County; derby@udel.edu

Barley harvest is proceeding rapidly and wheat harvest will begin very soon. To many growers, once small grains are harvested and the straw is baled or chopped and spread, the question that comes to mind is whether to go ahead and plant the next crop, generally soybeans, or to wait until rain to plant. This year in many situations, the soil is very low in available moisture. How do you go about deciding whether to plant or not? Following are some of the questions or factors, you should consider.

Is compaction more of a problem in drought years? Crop roots will not be able to penetrate compacted soil layers easily when the soil is dry. Roots that encounter compaction layers turn and grow horizontal and this severely limits the rooting zone available to the plant.

For growers with irrigation, irrigate before planting, plant, then irrigate again to ensure a good, strong stand. v

 


           Weather Summary

Week of June 3 to June 9

Rainfall:
0.01 inches: June 3
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 96F on June 8 to 78 F on June 5.
Lows Ranged from 73F on June 8 to 49F on June 6 .
Soil Temperature:
86 F average for the week.
(Soil temperature taken at a 2 inch depth, under sod)

Web Address for the U of D Research & Education Center:

http://www.rec.udel.edu


Compiled and Edited By:

Tracy Wootten

Extension Associate - Vegetable Crops


Cooperative Extension Education in Agriculture and home Economics, University of Delaware, Delaware State College and the United States Department of Agriculture cooperating, John C. Nye, Dean and Director. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, sex, disability, age or national origin.


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