Posts Tagged ‘abiotic stress’

High Temperature Effects on Peas

Friday, June 3rd, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Recently, we have had reports of pea fields with reduced seed set. Peas are best adapted to areas with warm days and cool nights. Extended high temperatures in excess of 85º F will cause yield declines in pea by reducing the number of seeds that are carried to harvest.

Experiments have shown that yields can be reduced by as much as 20% with a 5º increase in temperature from 85-90ºF. It has been shown that when peas are exposed to extended periods with high temperatures above 85º F that yields will decline greatly, especially in sensitive varieties. High temperatures in the last 10 days have been >85º F in much of the region.

The critical period where seed set will be reduced is late bloom. If the plant cannot support the full number of seeds due to high respiration and premature stomatal closure, seeds will abort or will not fill.


High Temperatures Can Affect Strawberry Yields

Friday, April 29th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Harvest of high tunnel plasticulture strawberries is well underway in the region and field harvest is beginning on plastic. Matted row strawberry harvest is still a few weeks off in most areas.

We have had several days in the mid 80s recently and this should remind growers that while the danger from frost should be over, effects of high temperatures can also greatly reduce strawberry productivity.

When daytime high temperatures reach a certain critical level, strawberries reproductive development will be affected. Flowering will be reduced or will stop altogether. The critical high temperature where flowering is affected and overall impact on flowering will vary with variety. Of the common strawberries being grown on plastic mulch in the annual system, ‘Camarosa’ is the most sensitive and will stop flowering and grow vegetatively when temperatures are above 86°F. ‘Chandler’ will handle somewhat higher temperatures. In matted row strawberry culture, it has been shown that strawberry size in ‘Earliglow’ is greatly reduced once temperatures reach the high 80s.

Growers wanting to maintain fruiting in years where May temperatures reach the high 80s or 90s should consider irrigating with overhead sprinklers during the day to cool plants (direct cooling and evaporative cooling). Use low volume sprinklers and set them to come on when air temperatures are above 85°F and come off when temperatures drop back below this level.


Blossom Damage in Strawberry Due to March Cold Snap

Thursday, April 14th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

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.


Early Transplanting of Warm Season Vegetables

Thursday, April 14th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

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.


Barley Frost Damage Hits in Kent Co.

Friday, April 8th, 2011

Richard Taylor, Extension Agronomist; and Phillip Sylvester, Kent Co., Ag Agent;

While checking out a barley field for possible manganese (Mn) deficiency problems, we discovered that the field had recently been damaged by freezing temperatures. Photos 1, 2, and 3 below show the typical whitening or bleaching of the leaf when temperatures drop below the critical level for barley at its current development stage. Photo 2 and 3 show the typical leaf tip bleaching but also show how freezing temperatures affect leaves differently depending on the stage of emergence of the leaf involved. Some leaves were affected only at the leaf tip while others were damaged around mid leaf leaving a whitened area in the middle of the leaf and green leaf at the tip and base of the leaf blade.

The question we can’t answer at this point with 100% certainty is whether the low temperatures caused pollen sterility in the developing seed head. The plants appeared to be at the Feekes 5 growth stage when the first node is just visible above the soil surface. We think that at this early stage damage will be limited to the leaf bleaching symptoms we observed. We won’t be able to know for sure until after heading when the anthers extrude from the florets and we can detect whether pollen release occurs. If pollen viability is impacted, the heads will not set grain and the heads will appear blank.

In the areas where Mn deficiency was observed, the leaf damage from the freezing temperatures was much worse causing significant injury to the barley plants (Photo 4). These plants will likely recover but yield will be much reduced.

Photo 1. Generalized tip burn on barley subjected to freezing temperatures following renewed spring growth and nitrogen application.

Photo 2. Leaf tip burn and mid-leaf frost injury showing stage of leaf emergence at the time of freezing temperatures.

Photo 3. Close-up view of leaf injury caused by freezing temperatures on barley. The growing point is just above the soil surface at this stage of growth.

Photo 4. Close-up view of severity of frost damage on Mn deficient plants.

And the Heat Goes On

Friday, August 13th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

In June we had 12 days with temperatures in the 90s, in July so far we have had 15 days with high temperatures 90°F or higher with 2 of those days at or over 100. What has this meant for vegetable crops in Delaware? First, yields are off in most crops from snap beans to sweet corn. The processing snap bean crop is one of the worst we have had in many years with low tonnage and split sets. Watermelon yields are variable with later planted fields with no middle set (crown and late, not much between). Most vegetable crops are at least 7 days earlier than normal with some running as much as 2 weeks early. We are likely to have a shortage of watermelons in late August and for the Labor Day market. Cantaloupe plantings are coming off early and together. And we have August to come – we need lower temperatures for our lima beans and other fall harvest crops to yield well.

Ozone Damage in Vegetables

Friday, August 6th, 2010

Elsa Sánchez, Associate Professor of Horticultural Systems Management, Penn State;

Reprinted from The Vegetable & Small Fruit Gazette, August 2010, Volume 14, No. 8, Penn State Cooperative Extension.

The heat wave we just experienced was brutal! It was tough to keep our crops well watered and take care of other management tasks in that heat. By the end of last week, we started getting reports of possible ozone damage on vegetables.

Symptoms of Damage
Ozone damage first occurs on older and mid-aged leaves with new growth generally being unaffected. Most commonly symptoms are found on the upper leaf surface, but with some plant species and cultivars it can be found on the lower surface as well. Symptoms start as small, irregular-shaped lesions that can be dark or light in color. With time, these lesions can grow into each other creating large dead areas. You may also notice stippling, bronzing or reddening of the leaves. The extent of the development of symptoms depends on the duration plants are exposed to ozone, the ozone concentration, the type and cultivar of crop grown and weather conditions. To see some pictures of ozone damage visit Symptoms can be confused with severe spider mite damage, phytotoxicity from pesticides, nutrient deficiencies, drought stress and some foliar diseases. Also, ozone damaged plants can be more susceptible to diseases. Extension educators can be contacted to help sort this out.

How Ozone Damages Plants
Ozone is an air pollutant which causes phytotoxicity when levels are high enough. Ozone enters leaves through stomata. From there it reacts with various substances in the leaves which yield toxic compounds.

Depending on how extensive the damage is, photosynthesis is reduced which can lead to decreased growth and yields. Plants also can mature quicker than normal. Plants respond differently to air pollutants, like ozone, with tomato, watermelon, squash, potato, string beans, snap beans, muskmelon, beets, carrots, sweet corn, peas, turnips and strawberries being considered more susceptible and cucumbers, pumpkins and peppers less susceptible.

How the Heat Wave May Have Played a Role
Weather conditions are one factor that contributes to the extent of ozone damage. High ozone levels are found when it is hot and sunny over large areas. Ozone also accumulates when air is not moving. Dennis Decoteau, a Penn State Researcher who studies air quality impacts on plants, recorded ozone concentrations high enough to damage plants last week. Additionally, when plants are under stress, such as from heat, they can be more susceptible to ozone damage.

Minimizing Damage
Maintaining healthy plants by limiting plant stress will help to minimize ozone damage. Careful water and nutrient management are a must. Timely irrigation, especially during heat waves, is critical. If symptoms are slight, the plants will likely outgrow the damage.

Effects of Ozone Air Pollution on Plants. 2010.

G. Johnson. 2008. Air Pollution Injury in Vegetable Crops.

G.J. Holmes and J.R. Schultheis. 2003. Sensitivity of watermelon cultigens to ambient ozone in North Carolina. Plant Dis. 87:428-434.

G. E. Brust. 2007. Air Pollution Effects on Vegetables. .

High Soil Temperature Effects on Stands in Seeded Vegetables

Friday, August 6th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Many vegetables for fall harvest are direct seeded in July and August. This is also the time of year with the highest soil temperatures. This summer, temperatures were in the 90s and even 100°F for days on end and this past week the heat was back again.

High soil temperatures can cause problems with direct seeded vegetables, even where irrigation has been applied. Small seeded, shallow planted crops are at highest risk of uneven stands due to high soil temperatures because soils are hottest nearest the surface (try walking on dry sand at the beach in the middle of the day with bare feet – ouch!)

There are also large differences between vegetable species on ability to germinate in high soil temperatures. Spinach and lettuce are notorious for having poor germination in high temperature soils. Some large seeded vegetables such as snap beans can also be affected.

Stand problems due to high soil temperatures are most likely in conventionally tilled ground and very sandy soils with low organic matter. Delays in germination may occur and germinating seeds may be killed. Roots of shallow seedlings may also be heat damaged in high temperature soils.

To prevent losses due to high temperature soils, irrigate prior to planting to moisten the soil and then again soon after planting to keep the soil moist. The more moisture in the soil, the more energy (from the sun) is needed to raise soil temperatures. For larger seeds, consider planting deeper when soil temperatures are high.

Dry to Wet Disorders in Vegetables and Fruits

Friday, July 16th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Most areas of Delaware received significant rainfall over the last 7 days. For example, Bridgeville had over 3.7 inches of rain, Dover, over 3 inches, Blackbird over 3.3 inches, Laurel 2.2 inches, and Greenwood, 3.2 inches. While this was welcome for soybeans and helped to stop further yield loss in corn, it was a mixed blessing in vegetables. Certainly, crops such as dry land lima beans have benefitted greatly as have non-irrigated corners of pivots (pickles and sweet corn especially). However, heavy rainfall after a long, hot, dry period can lead to certain disorders in other vegetables and fruits. Common problems include:

Fruit Cracking and Splitting
This is most common in ripening tomatoes, peaches, and melons but also can be found in other fruiting crops, especially those that were water stressed prior to the rains.

Edema is water blistering and is causes when the plant takes up more water than it is transpiring. This is seen as raised bumps on leaves, stems, and sometimes fruits. If water pressure is great enough, these raised bumps will burst leaving small blisters.

After heavy rains, in areas of the field that remain waterlogged, plants will wilt once the sun comes out. This is because roots are not functioning properly due to lack of oxygen. Wet conditions can also increase the susceptibility to root, crown, and stem rots due to organisms such as Pythium and Phytophthora, also leading to wilting.

Split Sets
Split sets are common in crops such as snap beans and lima beans where a crop under heat and moisture stress subsequently receives ample rain along with reduced heat. This induces re-flowering and a second pod or fruit set. Split sets complicate harvest timing as well as pest management programs in these crops.

Fruit Quality Reduction
Heavy rainfall along with cloudy weather can cause fruit quality problems in those fruits near ripening. Most common is reduced sugar content.

Problems With the Hot, Dry Weather

Friday, July 9th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

The excessively hot and dry weather is taking its toll on dryland field crops. While most vegetables are irrigated, we are still seeing heat and drought related problems. Some common problems are:

Sunscald is evident on many vegetables. This is especially the case where irrigation has not been able to keep up and plants have wilted for a period of time, exposing fruits. Dark colored fruits are most susceptible. Sunscald is most common on peppers, tomatoes, and cucumbers but also can be seen on watermelons, melons, and some squash. Exposed potato tubers are also susceptible. Sunscald is controlled by not allowing plants to wilt and having adequate leaf cover.

Blossom End Rot
Blossom end rot on peppers and tomatoes is common at this time due to the inability of plants to move enough calcium into expanding fruits, especially if plants are water stressed for periods of time. Blossom end rot increases in excessively hot weather. Blossom end rot can be reduced by addition of soluble calcium containing fertilizers and by irrigating so that plant demands are being met.

Leaf Curl
Plants such as tomatoes, peppers, and potatoes often react to hot weather by having increased amount of permanent leaf curling. No control measures are necessary.

Leaf Scorch
Leafy vegetables under heat and water stress often will have leaf edges that scorch. This also can be compounded by calcium deficiencies or reduction in calcium movement to the edges of rapidly expanding leaves. Many other vegetables will show leaf scorch symptoms. Having adequate irrigation management is critical to avoiding leaf scorch. Evaporative cooling from overhead irrigation can also help reduce leaf scorch.

Transplant Collapse
Late transplanted vegetables on black plastic mulch can collapse due to heat necrosis of stems touching the plastic mulch or by overheating of beds under the plastic so that roots are killed. Control by using white plastic mulch instead of black, using a larger planting hole to dissipate the excess heat, running overhead irrigation to cool the mulch, and keeping beds moist with drip irrigation.