Vegetables

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

 

Lima Beans.
Be sure to watch for spider mites on seedling stage lima beans, especially in areas of the state that have not been receiving adequate rainfall. Both field interiors as well as field edges should be examined for mites. Look for the white stippling along the veins on the underside of the leaves. A treatment should be considered when you first notice the stippling and you find 10-20 mites per leaflet. Kelthane or Capture (6.4 oz/A) have provided the best control in lima beans. The earliest planted fields should be scouted for lygus bugs and stinkbugs. Treatment should be considered if you find 15 adults and/or nymphs per 50 sweeps. Lannate, Capture or Mustang can be used if both species are present. The higher labeled rates of Capture (4 oz/A) and Mustang (4.3 oz/A) will be needed if stinkbugs are the predominant insect present.
 

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 and aphid infestations. If spider mite populations are high at the time of treatment, 2 sprays spaced 5 days apart will be needed. The threshold for mites is 20-30% infested crowns with 1-2 mites per leaf. Acramite (only one application per season), Capture, Danitol, Agri-Mek or Kelthane will provide control, but should be rotated to avoid the development of resistance. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Be sure to check runners carefully for aphids.  For a treatment to be effective, fields should be sprayed before you see significant leaf curling.  Be sure to watch for bees foraging in the area and avoid insecticide applications on blooming crops. 
 

Peppers.
Although corn borer catches are still generally light, we are starting to see an increase in moth catches. 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 a treatment for pepper maggot. If Orthene is used, it will also provide pepper maggot control. Otherwise, dimethoate should be added to the mix. High beet armyworm (BAW) moth catches have been reported from VA. Consultants have also found the first larvae in pepper fields. You will first notice the “shot-hole” feeding signs in the terminals. No threshold is available, so you need to watch for the first small larvae as well as their feeding signs. You will also need to use a product like Confirm, Spintor, Avaunt or Intrepid which provide good BAW control.
 

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 ⅓ to ½ if all stages of larvae are present. Avaunt + PBO, Actara, cryolite, Spintor,  Provado or newly labeled Rimon will provide control of larvae. We continue to see an increase in 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 this season; however, have not been 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.  We continue to find economic levels of green peach aphids in fields that did not receive Admire, Platinum or Tops MZ Gaucho at planting. A control will be needed if you find 2 aphids per leaf pre-bloom, 4 aphids per leaf post bloom and 10 aphids per leaf at 2 weeks from vine kill/harvest.  If melon aphids are found, the threshold should be reduced by ½.  If green peach aphid is the predominant species, Fulfill, Lannate, Monitor, Provado, or Vydate will provide control. If Fulfill is used, a penetrating surfactant is needed to achieve good coverage and achieve optimum control.

Snap Beans.
Continue to scout all seedling stage beans 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 ⅓. 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 fresh market silking sweet corn should be sprayed on a 5-day schedule except in the Milford area where sprays are needed on a 3 day schedule.  Since this information 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 silking sweet corn (http://www.udel.edu/IPM/traps/latestblt.html and http://www.udel.edu/IPM/thresh/silkspraythresh.html).  We are also starting to see the first fall armyworm larvae in whorl stage sweet corn. A treatment should be considered when 12-15% of the plants are infested. Since fall armyworm feed deep in the whorls, sprays should be directed into the whorls and multiple applications are often needed to achieve control.

 

 

Potato Maturity, Skinning, and Bruising: Vine Killing and Harvester Operation – Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

 

Moderate temperatures, especially with the relatively cool nights we have experienced, favor potato tuber bulking.  The sugars or carbohydrates formed during the day in the leaves through photosynthesis are not “burned up” as much through the respiration process.  In other words, a higher amount of carbohydrates can be accumulated in the tubers, rather than being used by the plant to keep it functioning.  While I’ve never done it, I often said our potato yields could be correlated with the average temperatures in June and early July.

 

Soon potato vine growth will slow and leaf senescence will increase, with the vines reaching the maximum size and then begin to decline.  Early maturing varieties will die back soon, while later maturing varieties will die back if the season is long enough, which is usually the case in Delaware.  During this period of decline, sugars and mineral nutrients in the vines become mobilized and translocated to the tubers.  Tuber growth will continue until the vines are completely dead.  At this point, 75 to 80% of the dry matter accumulated by the plant is in the tubers.  A chemical vine killer may be used to accelerate senescence. 

 

Vine killing not only hastens tuber maturation, often called hardening.  The outer skin, or periderm, forms from the outermost three or four cell layers of the tuber.  The collapsed walls of these cells form a barrier which prevents water loss from the tuber, protects it against pathogens, and helps limit bruising.

 

Tuber bruising costs potato growers across the country millions of dollars because it reduces raw product quality for processing.  In Delaware, where most of our acreage is destined for tablestock, there is not the direct linkage between the farm and the processor.  However, bruised potatoes cause great concern for fresh markets because bruised potatoes that end up in fresh pack containers present a poor image to the buyer and consumer.  Bruises can also give decay a place to start.

 

There are several types of Bruises.  Skinning occurs when the tubers are not completely mature.  A corky layer will form on the bruised area.  Cuts and scrapes result when potatoes strike a sharp edge or object during harvest, packing or handling.  Pressure bruise from the weight of the potatoes on themselves, especially when relative humidity is low.  Blackspot appears as a dark, semispherical spot in the tuber flesh beneath the skin 24-48 hours after impact on a hard surface.  Blackspot is a physiological disorder resulting from a serious of biochemical reactions leading to the production of a black pigment in the bruised flesh.  The injury may not be detected until the potato is peeled.  Potato varieties will differ in their susceptibility to Blackspot, but all varieties are more susceptible when soil moisture at harvest is low and the tubers are dehydrated.  Inadequate potassium may also increase the risk of Blackspot.

 

Allowing potatoes to reach full maturity helps reduce bruising injury.  Proper vine killing to speed maturity when an advanced harvest is desired is also important.  If the vine killing is done 10 to 14 days in advance, there will be enough time for increased skin development on the tubers.

 

There are three materials recommended for vine killing in Delaware:

ü      Desicate II (endothall) Apply 1.5 to 2 quarts/A 10 to 14 days before harvest.  Ammonium sulfate may be added. 

ü      Diquat 2SC at 1 pint/acre with a nonionic surfactant may be used.  It can be repeated in five days, if necessary.  Do not harvest for 7 days after treatment.

ü      Paraquat at 1-2 pints per acre with a non-ionic surfactant may be used.  Do not harvest until 3 days after treatment.  This may be the fastest kill, which could be problematic as to good hardening or “skin set.”

 

There are important directions and recommendations on the labels of each of these products.  Read and follow the directions carefully. 

 

With all of these, the proper adjustment, operation and maintenance of all parts of the harvester may be the most critical component of reducing injury.  Forward speed, chain speeds, and belt speeds should be adjusted to manufacturer’s recommendations.  Often, these adjustments need to be modified according to soil moisture conditions, crop maturity, and other field factors.

  

 

Vegetable Crop Diseases - Bob Mulrooney,

Extension Plant Pathologist, bobmul@udel.edu

 

IMPORTANT NOTICE - Late Blight.

I just received a reliable report that late blight was confirmed on tomatoes in Lancaster County, PA. Tomato growers in areas that have had rainfall will want to keep up their fungicide applications. Strains or genotypes of the late blight fungus that infect tomato are usually not very pathogenic on potato, but can infect potato leaves as well. Although conditions in Kent and Sussex County have not been very favorable for infection, areas of New Castle county and nearby Maryland may be similar to conditions in Lancaster county. So be on the lookout and keep up your preventative sprays.

 

Lima beans.

The State Department of Agriculture recently granted a section 24(c) label for the use of Phostrol in Delaware for control of downy mildew on lima beans caused by the fungus Phytophthora phaseoli. Nufarm Americas, Inc. petitioned the state for this label, which I supported with data from field plot work in 2001 and 2003. It has been very effective for the control of downy mildew. It has been labeled at 4 pts/A in 20 gal of water by ground and 5 gallons by air. Applications should be made every 7 days when conditions are favorable for infection. This product has to be used before symptoms of disease appear. It will not be effective if the disease is already present in the field. The mode of action is presumably that the product triggers the plant’s own defense mechanisms so that it protects itself from infection. It has no pre-harvest restriction and has a 4-hour restricted entry interval (REI ). I will expand on fungicide control programs for downy mildew control in upcoming issues of WCU.

 

 

Late Blight Advisory.

 

Disease Severity Value (DSV) Accumulation as of June 30, 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