Vegetables

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

 

Melons.

Continue to scout all melons for aphids, cucumber beetles, and spider mites. Economic levels of melon aphids have been detected and spider mite populations are building in a few fields. The threshold for mites is 20-30% infested crowns with 1-2 mites per leaf. 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. Fulfill, Lannate and Thiodan are labeled on melons and will provide melon aphid control. You should also watch carefully for cucumber beetles.

 

For growers transplanting some or all of their vine crops, the following article from Dr. Shelby Fleischer, entomologist of Penn State University, explains the rates for treating flats. "To control cucumber beetle invasion at transplanting, we recommend using Admire at a very low rate (0.02 ml/plant) to treat transplants about 1 day prior to planting in the field. To treat a flat of 200 transplants with Admire at this rate, a grower would need to dilute 4 ml (0.135 fl oz) of Admire in a volume of water sufficient to soak the soil mix evenly. This treatment will protect the plants for a short period of time (about 2 weeks) and after that should be followed by field application. [Water plants lightly after application to avoid leaching insecticide out of the media.] To help make other conversions, just multiply 0.02 ml per plant times the number of plants in your flat. For example, use 20 ml (0.7 fl oz) to treat 1000 transplants. (This rate is just a little higher than suggested for tomato transplants, which is 15 ml [or 0.5 fl oz] per 1000 transplants.) You can convert ml to fl oz by dividing ml by 29.6 (there is 29.6 ml in one fl oz). Be careful of burning the plants at higher rates. We observed burning of leaf margins at 0.04 ml/melon plant at the 2-leaf stage, although these plants did grow out of this in about 2 weeks."

 

Seed Corn maggot continues to be a problem in recently transplanted melons. Before transplanting, a broadcast application of diazinon should be incorporated 3 inches deep. The use of Admire or Platinum as a drip irrigation injection treatment has helped to reduce problems from seed corn maggot.

 

Peas.

Continue to sample for aphids. A treatment will be needed if you find 5-10 aphids per plant or 50 or more aphids per sweep. Dimethoate or Lannate will provide aphid control. Be sure to check the labels for application restrictions during bloom.

 

Peppers.

Since pepper transplants were set out last week, you should be sure to watch for thrips and corn borer activity. In years when corn planting is delayed, we often find corn borer larvae entering the petioles and main stems. Watch for egg masses and small larvae as well as check local moth catches in your area. Although no threshold has been established, a treatment with a pyrethroid may be needed if corn borer moth catches reach 10 moths per night, especially if you are using rye strips as wind breaks. We have also seen corn borer larvae move out of rye strips and attack tomatoes.  In general, 2 applications of a pyrethroid will be needed to achieve effective control. Thrips can cause damage in peppers by vectoring tomato spotted wilt virus and by causing direct plant damage. Although there are no available thresholds, a treatment may be needed if you see populations increasing. Baythroid, Capture, Spintor and Warrior will provide thrips control.

 

Potatoes.

Colorado potato beetle(CPB) adults, egg masses and the first small larvae can still be found in earliest emerged fields where an at-planting CPB material was not used.  A treatment should not be needed for adults until you find 25 beetles per 50 plants and defoliation has reached the 10% level. Once larvae are detected, the threshold is 4 small larvae per plant or 1.5 large larvae per plant.  Actara, cryloite, Spintor or Provado will provide control. Corn borer catches remain light; however ECB egg masses can be found in the earliest planted potatoes. A corn borer spray may be needed 3-5 days after an increase in trap catches or when we reach 700-degree days (base 50). Be sure to check our website (http://www.udel.edu/IPM/traps/latestblt.html) for the most recent moth catches in your area. Ambush, Baythroid, Furadan, Penncap, Pounce or Spintor will provide control. If you are scouting for infested terminals, the first treatment should be applied when 20-25% of the terminals are infested. Furadan or Monitor will provide the best control if you are waiting until you see infested terminals.  Potato leafhoppers populations remain light. 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. A pyrethroid, Actara or Provado will provide control. With the cooler weather, we have also seen an increase in potato aphid populations. Although we have rarely sprayed for potato aphids, the treatment threshold for aphids is 2 per leaf. Provado,  Monitor or Fulfill will provide aphid control.

 

Sweet Corn.

Flea beetles and cutworms are still active in seedling stage sweet corn. The treatment threshold for flea beetles is 5% infested plants. The cutworm threshold is 3% cut plants or 10% leaf feeding. Continue to sample any corn in the whorl stage for European corn borer larvae.  A treatment should be applied if 15% of the plants are infested. In recent years, Baythroid, Mustang, Penncap or Warrior have provided effective control.

 

 

 

Cool Temperatures and Wilting Transplants – Tracy Wootten, Extension Associate – Vegetable Crops, wootten@udel.edu; Derby Walker, Extension Agricultural Agent, derby@udel.edu

 

There have been numerous calls concerning wilting transplants in the field.  Weather conditions have not been favorable for plant growth.  Beginning May 1, there have been only 4 days out of 21 days that the average air temperature was greater than 65°F. The minimum temperature for watermelon growth is 65°F, with optimum temperatures for growth at 70-85°F. 

 

This growing season has not been forgiving.  Under the current growing conditions, even strong transplants would have a tough time becoming established in the field.  Last week we mentioned transplants that were wilting from being planted too shallow with inadequate soil coverage of the plug mix.  Other observations since then include: root balls that were damaged as they were pulled from the trays at planting, leaving a smaller, damaged root system; plants are leggy with too much plant at the top for the root system to keep up; and some transplants may have been planted in the field too early, before the root system can support the plant under field conditions.

 

Transplants are also wilting from being planted too deep or are submerged in water.  Some transplants have been planted up to the cotyledon leaves.  This can happen when the soil is over saturated at planting or if you try to compensate for some of the leggy transplants that have resulted from the cool, cloudy weather during transplant production.  In a dry year, these transplants would probably have been fine, but are too deep in a wet year.  Cucurbits will not form roots on the stem as tomatoes will. Thus, the extra wet soil around the stem induces extra stress on the plant, leading to reduced oxygen and possible disease infection. Watermelons can not tolerate wet conditions for an extended period of time.  They do not like to have “wet feet”.  Roots become starved for oxygen and eventually die.  Problems seemed to be more severe in heavier soils that do not drain well.  Even high, sandy areas have been too wet after the large rain we received. 

 

What to do?  Planting in these conditions can be tricky.  People transplanting should adjust their planting depth to current soil conditions.  This may mean planting at a shallower depth in the low areas, but still covering the plug mix. The science of transplanting is getting enough soil around the transplant to keep it from popping out of the ground.  The art of transplanting is not getting too much soil around the plant to suffocate it.   The amount of water delivered to each transplant may also need to be adjusted. 

 

So far this season, we have experienced transplants infected with seed corn maggot, plants with discoloration of the roots or stems indicating possible disease infection, or otherwise healthy plants that have wilted.  No insects are present or no obvious symptoms of disease (discoloration of the roots or stem). Plants have a strong stem with collapsed leaves. The growing point is still active.  If there is discoloration of the roots or stems, plants should be examined for seed corn maggot damage or possible disease. See related article under Vegetable Diseases.

 

 

 

Plant on the left is from a low area of the field with heavy soil. Note: collapsed leaves, growing point still active and the lack of a healthy root system.  The root system did not hold the soil together after removal.  Plants on the right were from a high, sandy area.  The plant on the right is healthy with no visible symptoms.  The middle plant has a collapsed leaf, but the root system is better than the one from the wet area of the field.

 

Photo of healthy transplant with new root growth.

 

When to replant?  Our current recommendation would be to wait until we receive warm, sunny weather.  Current transplants have wilted leaves with the next true leaf emerging.  There is no way of knowing at this time which plants will recover.  Unless the weather changes, any transplants placed in the field at this time with sit until we do receive better growing conditions. 

 

 

      Air Temperatures (°F) May 1-21, 2003

 

Date	High	Low	Average
5/1/2003	81	52	66.5
5/2/2003	76	60	68
5/3/2003	65	43	54
5/4/2003	61	39	50
5/5/2003	56	33	44.5
5/6/2003	66	50	58
5/7/2003	80	49	64.5
5/8/2003	73	53	63
5/9/2003	64	53	58.5
5/10/2003	72	55	63.5
5/11/2003	83	63