Posts Tagged ‘19:4’

Blossom Damage in Strawberry Due to March Cold Snap

Thursday, April 14th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Plasticulture strawberry growers reported significant damage to early blooms during the cold snap between March 27-29, even with heavy weight floating row covers in place. Temperatures as low as 21°F were recorded in some locations. When temperatures at flower level have the potential to drop below 30°F for extended periods under row covers, then a combination frost protection approach of row covers combined with sprinklers is needed to avoid freeze losses.

 

Primocane Blackberries

Thursday, April 14th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Until recently, commercially available blackberries were floricane types, that is, they fruit on last year’s canes. Six years ago, the University of Arkansas released their first primocane blackberries, Prime-Jim and Prime-Jan. Primocane blackberries fruit on current season canes, allowing for blackberry production from mid-summer through frost. In subsequent years they have the potential for two-season fruiting – in early summer on overwintered canes and as a late summer and fall crop on current season primocanes – as much as 6 months of production. The first two releases (Prime Jim and Jan) did not have sufficient fruit quality to be used for commercial production and were mostly recommended for home gardens. In 2009, Dr. John Clark at Arkansas released Ark-45, a primocane blackberry which did have good fruit quality and commercial potential. It is recommended for trial in Delaware. Unfortunately it is still thorny which will limit its use. The good news is that Dr. Clark is working on thornless primocane blackberries. We will be testing some of his advanced thornless primocane selections at the UD research station at Georgetown (planted this spring).

What is exciting about primocane blackberries is that they offer extended production potential into the fall. They also offer flexibility in production as they can be treated as a two season fruiting crop summer and late summer-fall (overwintered and primocane production) or single season (primocane only) production late summer-fall. Blackberries are generally well adapted to Delmarva conditions but will shut down if temperatures stay in the 90s for extended periods. Primocane blackberries will be flowering and fruiting much of the time in the cooler late summer and fall. Stay tuned as we follow these blackberry advances.

 

Pea Herbicides

Thursday, April 14th, 2011

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Weed control options remain limited for processing peas. Pursuit, at 1.5 to 2.0 fluid ounces per acre, needs to be used as a pre-plant incorporated or preemergence treatment and is used primarily for broadleaf weeds. Preemergence applications of Command (8 to 16 fl oz) or Dual (0.5 to 1 pt/A) are labeled for control of annual grasses and some broadleaf weeds. Basagran and Thistrol are labeled for postemergence control of broadleaf weeds. Apply Basagran at 1.5 to 2 pints per acre after peas have more than three pairs of leaves. Do not add oil concentrate. Select, Assure II, Targa, or Poast can be used for postemergence grass control.

 

Early Transplanting of Warm Season Vegetables

Thursday, April 14th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Earliest plantings of watermelons, cantaloupes, summer squash, and tomatoes will begin in the next 10 days. First transplanting of crops such as peppers and eggplant will begin in early May. One of the characteristics that all of these crops have in common is that they are warm season vegetables that are sensitive to cold temperatures, both in the root zone and above ground. There has been a tendency to risk earlier and earlier plantings as growers try to hit the early market. Over the years, many of our early plantings of summer vegetables have suffered because of early cold damage and inadequate provisions to protect plants.

For early transplanted warm season vegetables choose the lightest ground that warms up quickly. Plant higher sections in the field first. Avoid areas that receive any shade from woods or hedgerows. Early fields should be protected from extreme wind and should not have frost pockets. Rye windbreaks planted between each bed are desirable for early plantings because they limit heat transfer by wind. If no rye windbreaks have been planted, then consideration should be given to using row covers to protect the plants – either clear slitted or perforated low tunnels or floating row covers. Even where windbreaks have been used, row covers may be necessary for extremely early plantings.

Lay plastic mulch well ahead of time to warm soil. Black plastic mulch should have excellent soil contact. Firm beds and tight mulch are much more effective in warming soils. Make sure that there is good soil moisture when forming beds and laying plastic because soil water will serve as the heat reservoir during cold nights.

When producing transplants, use larger cell sizes and grow plants so that they have well developed roots in those cells for the first plantings. Large cell sizes will perform better than small cells in early plantings. Careful attention needs to be paid to hardening off warm season vegetable transplants that will be planted early. Gradual acclimation to colder temperatures will reduce transplant shock. Do not transplant tender, leggy plants or plants coming directly out of warm greenhouse conditions for these early plantings.

Watch extended weather forecasts and plant at the beginning of a predicted warming trend. Monitor soil temperatures in plastic beds and do not plant if they are below 60°F. Soil temperature in beds should be measured at the beginning of the day when at the coolest. When soil temperature conditions are not favorable, wait to plant. Avoid planting in extended cloudy periods, especially if plants have come out of the greenhouse after an overcast period. These plants will not perform well. Extra caution should be taken to minimize root injury during transplanting. When transplanting, make sure that there is good root to soil contact and there are few air pockets around roots.

In years with cold, cloudy, windy weather after transplanting, we have had large losses of transplants in the field. It is critical to have warm soil conditions after transplanting to allow roots to grow out into the bed quickly. In cold, cloudy conditions, plants shut down physiologically, little root growth occurs, and the existing roots on the transplant do not function well. If there is any wind, plants lose more water than they can take up and they die due to desiccation. This is accelerated when the sun does come out – the first sunny day after an extended cold, cloudy period is when you will see the most wilting of weakened transplants.

If cold weather occurs after transplanting, warm season vegetables vary in their ability to tolerate adverse weather after being set out. Tomatoes will stop growth but will grow out without much damage once warm weather returns. Summer squash and cucumber transplants may be temporarily stunted but generally grow out of the condition. Watermelons will hold if they have been hardened off properly. Cantaloupes can be stunted if exposed to excessively harsh early conditions. Peppers and eggplants will not put on any root growth until temperatures are warm enough. If stunting occurs on any of these warm season vegetables, you may lose the early advantage you were seeking. In addition, remember that all of these vegetables are susceptible to frost damage and will be killed by a late freeze.

 

Vegetable Crop Insects – April 15, 2011

Thursday, April 14th, 2011

Cabbage
Continue scouting fields for imported cabbage worm and diamondback larvae as soon as plants are placed in the field. With a few days of warm temperatures, we will see an increase in moth egg laying activity. As a general guideline, a treatment is recommended if you find 5% of the plants infested with larvae.

Peas
Be sure to sample peas for pea aphids as soon as small seedlings emerge. On small plants, you should sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. As a general guideline, a treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. Be sure to check labels for application restrictions during bloom.