Vegetables

Update on Post-Emergence Weed Control in Spinach – Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

Stinger is labeled as a post-emergence herbicide for use on spinach.  It can be applied when the spinach is in the 2 to 5 leaf stage of growth.  It is useful for control of Canada thistle, sow thistle, black nightshade, clover, cocklebur, common groundsel, jimsonweed, prickly lettuce, pineappleweed, and ragweed.  Check the label for the proper rate for each weed species.  Scouting fields early for weed escapes is important to time Stinger applications for early weed control.

 

 

 

Downy Mildew on Cucurbits – Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

 

Over the past few weeks, we have written much about the control of Downy mildew on cucurbits.  It has been devastating, with serious yield loss on watermelons, significant damage to pumpkin vines, and very serious yield loss and quality damage to pickling cucumbers.  In the case of pickles, even with good yields at the beginning of the season, final production may only approach 50% of intended production.

 

With the innoculum coming to us early in the season and in apparently unprecedented amounts, this threat was compounded by cool, wet weather that favored the development of the disease.  In the 46 days between July 1 and August 15, it rained 28 days; or 60% of the days experienced rain.  There were two stretches of six consecutive days of rain during this time frame.  There were no days in this period with temperatures above 90^oF at the University of Delaware Research & Education Center’s weather station near Georgetown.

 

As reported earlier, a period of at least six hours of 100% relative humidity at the leaf surface is required for the disease organism to produce sporangia.  We certainly had extended periods of these conditions, which helped launch and maintain the epidemic of Downy mildew.

 

Some observers have inquired about the appearance of the plants and possible fertility deficiencies.  The pale, weakened appearance is a result of the Downy mildew, not plant nutrition problems.  The rates applied this year are consistent with previous years, when vine growth was aggressive, in fact, perhaps too aggressive.  We have one field with over 175 pounds/A of nitrogen applied in an attempt to stimulate the plant, and are not seeing any significant response.

 

Many fields still exhibit the symptoms and damage continues.  However, we are seeing some plantings that were sprayed frequently and often, holding their own.  While we work towards solutions for this year’s crop, we are turning our attention to avoiding and preventing a similar situation next year.  Although in the unlikely event the weather pattern repeats itself, the battle will be engaged again.

 

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

 

Cabbage.

Continue to sample fields for diamondback and cabbage looper larvae. Economic levels can now be found.  A treatment should be considered if you find 5% of the plants infested and before they move into the hearts of the plants. If both species are present, Avaunt, a Bt, Proclaim or  Spintor  will provide control. If cabbage looper is the predominant species, a pyrethroid, Intrepid, or Confirm  will also provide control.
 

Lima Beans.
Continue to scout for  lygus bugs and stinkbugs as soon as pin pods are present . Treatment should be considered if you find 15 adults and/or nymphs per 50 sweeps. Since earworm continues to be found in lima bean fields, be sure to scout fields with pin pods for corn earworm. A treatment will be needed if you find one corn earworm larvae per 6 ft of row. Capture, Lannate, Mustang or Warrior will provide earworm control. The higher rates may be needed if population levels are high and worms are large at the time of treatment.

 

Peppers.
Be sure to maintain a 5-7 day spray schedule for corn borer, corn earworm, beet armyworm and fall armyworm control.  

 

Snap Beans.
At this time, all fresh market and processing snap beans will need to be sprayed for corn borer and corn earworm control from the bud stage through harvest. Remember, Orthene provides poor corn earworm control. Since trap catches change quickly and we are seeing another spike in corn earworm moth catches, 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). 

 

 

Spinach.
Since webworm and beet armyworm moths are both actively laying eggs, be sure to watch for both worm pests as soon as plants emerge.  Controls should be applied when worms are small and before they have moved deep into the hearts of the plants. Also, remember that both insects can produce webbing on the plants. Since beet armyworms are more difficult to control, chemical selection is important. Confirm, Intrepid or Spintor will be needed for beet armyworm control. If webworms are the predominant species, permethrin, Confirm (8 oz/acre),or Intrepid (8-10 oz) should be used. Generally, at least 2 applications are needed to achieve control of webworms and beet armyworm.

 

Sweet Corn.
With the recent increase in corn earworm trap catches, all fresh market silking sweet corn should be sprayed on a 2-day schedule.  Be sure to check trap catches frequently. You can check trap catches and treatment decision guidelines on our website (http://www.udel.edu/IPM/traps/latestblt.html and http://www.udel.edu/IPM/thresh/silkspraythresh.html).

 

 

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

Lima beans.

Downy Mildew Alert. Downy mildew, caused by Phytophthora phaseoli, was positively identified in two samples from the Frederica-Bowers Beach area in Kent County. As we had stated before the weather has been very favorable for infection and continues to be favorable. Growers with beans that have pods should be applying protective fungicides for downy mildew. Remember that there are three diseases that can infect pods and may look similar namely, downy mildew, lima bean pod rot caused by Phytophthora capsici and white mold caused by Sclerotinia. If you see infected pods it is important that you get the disease correctly identified before applying a control. Fungicides for white mold and downy are very different and one fungicide will not control both diseases. White mold is controlled with Topsin M, Rovral, or Endura. Downy mildew is controlled by growing resistant varieties and applying fungicides preventatively. In order of effectiveness, Ridomil Gold/Copper is the best and most costly and is recommended if downy is found in the field followed by a copper spray 7 days later. It is also great preventatively. Phostrol as mentioned in earlier issues is also available and is an excellent preventative fungicide if used according to the label, 4 pts/A at weekly intervals. Phostrol will not control downy if infection has already occurred. Copper sprays (Champ DF and Kocide 2000 at 2.0 lb/A, Cuprofixx 3 lb/A) have also performed very well when used preventatively and weekly.

 

          

Downy mildew on lima pod.                     Downy mildew on pin pods.

 

 

 

 

LATE BLIGHT ADVISORY.  NOTE: This will be the last potato disease advisory.

 

Disease Severity Value (DSV) Accumulation as of August 18, 2004 is as follows:

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

 

Date	Daily DSV	Total DSV	Spray Recommendation
7/19	1	114	5-day
7/22	2	116	7-day
7/23	2	118	7-day
7/24	9	127	7-day
7/26	5	132	7-day
7/27	11	143	5-day
7/29	2	145	7-day
7/30	10	155	7-day
8/2	4	159	7-day
8/3	2	161	7-day
8/4	2	163	5-day
8/6-8/11	0	163	10-day
8/11	1	164	7-day
8/12	4	168	5-day
8/13	2	170	5-day
8/14	4	174	5-day
8/15	3	177	5-day
8/16	2	179	5-day
8/17	2	181	5-day

 

Application rates for protectant fungicides (Dithane, Bravo, etc.) should be at the high end of the rate with the amount of foliage present. For specific fungicide recommendations, see pages F132-33, 2004 Delaware Commercial Vegetable Production Recommendations Book. EB 137.

 

No late blight has been seen in DE-MD-NJ area on potatoes.

 

Note:  Late blight has been confirmed on tomato in Burlington and Sussex counties in NJ and is present in southeast PA on tomato as well. Growers with late potatoes and those that may have tomatoes nearby should continue to spray and scout for symptoms. There have been no new reports on tomato from these areas.

 

 

 

Field Crops

 

 

Field Crop Insects - Joanne Whalen, Extension  IPM Specialist;