Posts Tagged ‘vegetable crop management’

Using Winter Kill Cover Crops as a Part of Your Vegetable Cropping System

Friday, August 24th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Cover crops that will put on significant growth in the fall and then die during the winter can be very useful tools for vegetable cropping systems and the University of Delaware, University of Maryland, and other universities in the region have been conducting research on a number of these winter killed crops for use with vegetables.

Winter killed cover crops that are late summer and fall planted include spring oats, several mustard species, and forage and oilseed radish. Earlier planted summer annuals (millets; sorghums, sudangrasses, and hybrids; annual legumes such as sun hemp or forage soybeans; buckwheat and many others) can also be used as winter killed species. Timing of planting will vary according to the species being used and winter killed species selection will depend on when fields will be available for seeding. Spring oats, mustards, and radishes can be planted from late August through September. Once into October, they do not put on adequate fall growth. Summer annuals should be planted in late July or during August for use in a winter killed system to obtain sufficient growth.

The winter of 2011-2012 was extremely mild and gave us a good look at issues that occur when crops that normally winter kill do not. In our plots at the Georgetown, DE research farm last winter, forage radish, oilseed radish, spring oats, and edible greens type mustard (Tendergreen) did not winter kill completely. All the biofumigant mustards (Pacific Gold, Idagold, Caliente, and Kodiak) winter killed completely (as did summer annuals).

The following are several options for using winter killed species with vegetables:

1) Compaction mitigation for spring planted vegetables. Where there are compacted fields, the use of forage radishes has worked very well as a winter killed cover crop by “biodrilling”. The extremely large taproot penetrates deep into the soil, and after winterkilling, will leave a large hole where future crop roots can grow. Oilseed radish also provides considerable “biodrilling”. Winter killed radishes works well with spring planted crops such as peas, early sweet corn, and early snap beans.

2) Early planted vegetables. A wide range of early planted vegetables may benefit from winter killed cover crops. For example, peas no-till planted or planted using limited vertical tillage after a winter killed cover crop of forage radish, oilseed radish, or winter killed mustard have performed better than those planted after conventional tillage. Early sweet corn also has potential in these systems as do a wide range of spring vegetables. Winter killed radishes and mustards also have the advantage of outcompeting winter annual weeds leaving relatively weed free fields and also in recycling nutrients from the soil so that they are available in the spring for early crops (decomposition has already occurred).

3) Mixed systems with windbreaks for plasticulture. By planting planned plasticulture bed areas with winter killed cover crops and areas in-between with cereal rye you can gain the benefits of these soil improving cover crops and eliminate the need make tillage strips early in the spring. The winter killed areas can be tilled just prior to laying plastic.

4) Bio-strip till. By drilling one row of forage or oilseed radish and other adjacent rows with rye or other small grains, you can create a biodrilled strip that winter kills and that can be no-till planted into the spring without the need for strip-till implements. This opens up dozens of options for strip tilling (seed or transplanted) spring vegetables.

Vegetable Fungicide Updates for 2012

Thursday, March 29th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

The following is a very brief overview of recent fungicide registrations and new updates that may be of use to vegetable growers in 2012. This is not meant to be a comprehensive list. Also, I have not run research trials for most of these product uses, and therefore cannot say anything about efficacy in comparison to other products. Remember to follow all label directions carefully. Before use, check each label for rates, information on resistance management, tank mix incompatibilities and other information.

  • · Prophyte and some other phosphorous acid fungicides are available for use on bean cottony leak (Pythium cottony leak).
  • · Quintec now has a Section 2ee label for the suppression of bacterial leaf spot on pepper in some states in the mid-Atlantic (including DE and MD, but not PA).
  • · Both chlorothalonil and Manzate Pro Stick labels have added anthracnose fruit rot on pepper.
  • · The Ranman label now includes spinach white rust as well as club root and downy mildew of cole crops (brassicas).
  • · Quilt Xcel and Stratego YLD are labeled for sweet corn rust.
  • · A new OMRI approved copper, Nordox, has a broad label that includes many vegetables and use in the greenhouse on some crops.
  • · Quash fungicide is labeled on potato and sweet potato for many diseases including early blight and white mold.
  • · A label expansion for Cabrio lists management of stem rots caused by Rhizoctonia and Sclerotinia and Southern blight (Sclerotium rolfsii) on tomato, pepper and eggplant.
  • · Fontelis has received a label for many vegetables including brassicas (Alternaria, gray mold, powdery mildew, Sclerotinia); tomato and other fruiting vegetables (early blight, gray mold, powdery mildew, Septoria leaf spot, etc.); Leafy vegetables (Alternaria, Cercospora, Septoria, etc.); Legume crops (Alternaria, anthracnose, Ascochyta, Botrytis, etc.); and some root vegetables (early blight, Cercospora leaf spot, Sclerotium rolfsii, etc.)
  • · Luna Experience has received a label for use on watermelon in DE and the label is pending in MD. Diseases on the label include gummy stem blight, anthracnose, and powdery mildew.

Vegetable Crops are Off to an Early Start

Thursday, March 29th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; & Emmalea Ernest, Extension Associate-Vegetable Crops;

Asparagus harvest began last week which is four weeks early. Pea planting is ahead of schedule with heat units accumulating much more rapidly than the thirty year average making it likely that harvest will not extend past June. Peas have emerged rapidly and stands look very good. Average soil temperatures have already been in the mid 60s. Some fresh market sweet corn growers have their first and second plantings in already and sweet corn under plastic has emerged and is growing fast. Plastic mulch laying for summer crops is already underway. As we progress into April, a concern will be the potential for frosts and freezes with advanced crops.

The earliest peas will start flowering at less than 675 heat units and will be at full flower at 775 heat units. Currently, peas planted on February 25 have accumulated 306 heat units. In 2011 during the same period only 181 heat units accumulated. If accumulations continue at an accelerated pace and peas flower early, there is increased risk for frost damage to flowers in early plantings, causing reduced yields, and split sets.

Early planted sweet corn can also be at higher risk this year of frost damage. If the sweet corn growing point is not out of the ground and a freeze occurs, the emerged leaves will be injured but the plants can continue to grow. The growing point of sweet corn is still below or at ground level until the 5-6 leaf stage and is therefore protected against frost injury. If a frost or freeze event does occur with sweet corn, wait 3-4 days to evaluate. If you seed signs of regrowth, the sweet corn can recover. If regrowth is not evident, start splitting the stems of a sample of plants and look at the growing point. If it is firm and white or cream colored it is still alive. If it is soft, water soaked, or gray in color, it has died and you will lose some stand.

Processing sweet corn planting will begin in the next 2 weeks. It is interesting to note that the industry is moving to supersweet varieties for processing. In the past, our recommendations were to avoid early planting of supersweets and wait until soil temperatures were above 65° F, because these varieties tended to have less seed vigor. In 2010 and 2011 we planted supersweet variety trials on April 12. Surprisingly, a number of the supersweet varieties we tested had emergence rates over 90%. This suggests that high quality seed of supersweet varieties with demonstrated cold tolerance can probably be planted earlier, before soil temperatures reach 65°F. Detailed reports on the 2010 and 2011 trials are available online at This year, early April supersweet plantings may be justified, given that soils have already warmed substantially.

Some rye windbreaks used for watermelon and other vegetable protection have already reached full height and are heading out. Growers may have to kill windbreaks much earlier than normal or realize that seed will likely set which is a problem if rotating into wheat or barley (seed mixing with rye next year). Forage radishes and spring oats did not fully winter kill this year.

As we go into next week, highs are forecast in the 60s and 70s. However the extended forecast for both 6-10 and 8-14 days from NOAA is for “enhanced odds for below average temperature along the Mid-Atlantic”

Cover Crops that Did Not Winter Kill

Friday, March 2nd, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist;

With the mild winter, many cover crops have not fully winter killed including fall planted spring oats, forage radish, and some mustard species. For vegetable growers seeking to have early areas for spring planting, this will require that these cover crops be killed by herbicides, low mowing, or tillage. This will also limit the potential to no-till vegetables into these areas.

Flooding and Vegetables

Friday, August 26th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

There is still considerable acreage of watermelons, sweet corn, pumpkins, beans, cabbage, potatoes, and other fresh market vegetable crops in the field on Delmarva. On the processing side, the majority of lima beans have yet to be harvested and there are significant acres of pickles, snap beans, and other processing crops in the field. Many of these crops will be at risk in the coming days due to hurricane Irene.

A late summer hurricane or tropical storm with both wind damage and excess rain can cause major issues in vegetable crops, most notably:

● Damage due to flooded soils in all vegetable crops

● Increased disease incidence in all vegetable crops

● Lodging damage in crops like sweet corn

Other articles will address diseases in with excess rainfall. I will focus on flooding effects on the physiology of vegetable plants.

Flooded and Waterlogged Soils
In flooded soils, the oxygen concentration drops to near zero within 24 hours because water replaces most of air in the soil pore space. Oxygen diffuses much more slowly in water filled pores than in open pores. Roots need oxygen to respire and have normal cell activity. When any remaining oxygen is used up by the roots in flooded or waterlogged soils, they will cease to function normally. Therefore, mineral nutrient uptake and water uptake are reduced or stopped in flooded conditions (plants will often wilt in flooded conditions because roots have shut down). There is also a buildup of ethylene in flooded soils, the plant hormone that in excess amounts can cause leaf drop and premature senescence.

In general, if flooding or waterlogging lasts for less than 48 hours, most vegetable crops can recover. Longer periods will lead to high amounts of root death and lower chances of recovery.

While there has not been much research on flooding effects on vegetables, the following are some physiological effects that have been documented:

● Oxygen starvation in root crops such as potatoes will lead to cell death in tubers and storage roots. This will appear as dark or discolored areas in the tubers or roots. In carrots and other crops where the tap root is harvested, the tap root will often die leading to the formation of unmarketable fibrous roots.

● Lack of root function and movement of water and calcium in the plant will lead to calcium related disorders in plants; most notably you will have a higher incidence of blossom end rot in tomatoes, peppers, watermelons, and several other susceptible crops.

● Leaching and denitrification losses of nitrogen and limited nitrogen uptake in flooded soils will lead to nitrogen deficiencies across most vegetable crops.

● In bean crops, flooding or waterlogging has shown to decrease flower production and increase flower and young fruit abscission or abortion.

● Ethylene buildup in saturated soil conditions can cause leaf drop, flower drop, fruit drop, or early plant decline in many vegetable crops.

Recovering from Flooding or Waterlogging
The most important thing that you can do to aid in vegetable crop recovery after floods or waterlogging is to open up the soil by cultivating (in crops that still small enough to be cultivated) as soon as you can get back into the field. This allows for oxygen to enter the soil more rapidly. Nutritionally, sidedress with 50 lbs of N where possible.

In fields that are still wet, consider foliar applications of nutrients. According to Steve Rieners at Cornell “Use a low salt liquid fertilizer to supply 4 to 5 lb nitrogen, 1 lb phosphate (P2O5) and 1 lb potash (K2O) per acre. Since nitrogen is the key nutrient to supply, spraying with urea ammonium nitrate (28 % N solution) alone can be helpful. These can be sprayed by aerial or ground application. Use 5 to 20 gallons of water per acre. The higher gallons per acre generally provide better coverage”. As with all foliar applications, keep total salt concentrations to less than 3% solutions to avoid foliage burn.

Cover Crops for Vegetable Rotations Revisited

Friday, August 12th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

August is here and it is time to consider late summer and fall cover crop options for vegetable rotations. Cover crop planting windows vary with crop and timely planting is essential to achieve the desired results. Here are some reasons to consider using cover crops in vegetable rotations:

Return organic matter to the soil. Vegetable rotations are tillage intensive and organic matter is oxidized at a high rate. Cover crops help to maintain organic matter levels in the soil, a critical component of soil health and productivity.

Provide winter cover. By having a crop (including roots) growing on a field in the winter you recycle plant nutrients (especially nitrogen), reduce leaching losses of nitrogen, reduce erosion by wind and water, and reduce surface compaction and the effects of heavy rainfall on bare soils. Cover crops also compete with winter annual weeds and can help reduce weed pressure in the spring.

Reduce certain diseases and other pests. Cover crops help to maintain soil organic matter. Residue from cover crops can help increase the diversity of soil organisms and reduce soil borne disease pressure. Some cover crops may also help to suppress certain soil borne pests, such as nematodes, by releasing compounds that affect these pests upon decomposition.

Provide nitrogen for the following crop. Leguminous cover crops, such as hairy vetch or crimson clover, can provide significant amounts of nitrogen, especially for late spring planted vegetables.

Improve soil physical properties. Cover crops help to maintain or improve soil physical properties and reduce compaction. Roots of cover crops and incorporated cover crop residue will help improve drainage, water holding capacity, aeration, and tilth.

There are many cover crop options for late summer or fall planting, including:

Small Grains
Rye is often used as a winter cover as it is very cold hardy and deep rooted. It has the added advantage of being tall and strips can be left the following spring to provide windbreaks in crops such as watermelons. Rye makes very good surface mulch for roll-kill or plant through no-till systems for crops such as pumpkins. It also can be planted later (up to early November) and still provide adequate winter cover. Wheat, barley, and triticale are also planted as winter cover crops by vegetable producers.

Spring oats may also be used as a cover crop and can produce significant growth if planted in late August or early September. It has the advantage of winter killing in most years, thus making it easier to manage for early spring crops such as peas or cabbage. All the small grain cover crops will make more cover with some nitrogen application or the use of manure.

To get full advantage of small grain cover crops, use full seeding rates and plant early enough to get some fall tillering. Drilling is preferred to broadcast or aerial seeding.

Both perennial and annual ryegrasses also make good winter cover crops. They are quick growing in the fall and can be planted from late August through October. If allowed to grow in the spring, ryegrasses can add significant organic matter to the soil when turned under, but avoid letting them go to seed.

Winter Annual Legumes
Hairy vetch, crimson clover, field peas, subterranean clover, and other clovers are excellent cover crops and can provide significant nitrogen for vegetable crops that follow. Hairy vetch works very well in no-till vegetable systems where it is allowed to go up to flowering and then is killed by herbicides or with a roller-crimper. It is a common system for planting pumpkins in the region but also works well for late plantings of other vine crops, tomatoes and peppers. Hairy vetch, crimson clover and subterranean clover can provide from 80 to well over 100 pounds of nitrogen equivalent. Remember to inoculate the seeds of these crops with the proper Rhizobial inoculants for that particular legume. All of these legume species should be planted as early as possible – from the last week in August through the end of September to get adequate fall growth. These crops need to be established at least 4 weeks before a killing frost.

Brassica Species
There has been an increase in interest in the use of certain Brassica species as cover crops for vegetable rotations.

Rapeseed has been used as a winter cover and has shown some promise in reducing levels of certain nematode in the soil. To take advantage of the biofumigation properties of rapeseed you plant the crop in late summer, allow the plant to develop until early next spring and then till it under before it goes to seed. It is the leaves that break down to release the fumigant-like chemical. Mow rapeseed using a flail mower and plow down the residue immediately. Never mow down more area than can be plowed under within two hours. Note: Mowing injures the plants and initiates a process releasing nematicidal chemicals into the soil. Failure to incorporate mowed plant material into the soil quickly, allows much of these available toxicants to escape by volatilization.

Turnips and mustards can be used for fall cover but not all varieties and species will winter over into the spring. Several mustard species have biofumigation potential and a succession rotation of an August planting of biofumigant mustards that are tilled under in October followed by small grain can significantly reduce diseases for spring planted vegetables that follow.

More recent research in the region has been with forage radish. It produces a giant tap root that acts like a bio-drill, opening up channels in the soil and reducing compaction. When planted in late summer, it will produce a large amount of growth and will smother any winter annual weeds. It will then winter kill leaving a very mellow, weed-free seedbed. It is an ideal cover crop for systems with early spring planted vegetables such as peas.

Oilseed radish is similar to forage radish but has a less significant root. It also winter kills.

Brassicas must be planted early – mid-August through mid-September – for best effect.

Mixtures of rye with winter legume cover crops (such as hairy vetch) have been successful and offer the advantage, in no-till systems, of having a more rapidly decomposing material with the longer residual rye as a mulch.

Stress in Vegetables

Friday, July 15th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

In troubleshooting vegetables in the summer months, we see fields where the major symptom is an overall lack of vigor and this poor vigor is due to one or more stress factors. Hot weather makes this stress more pronounced. Pests such as root and crown rot fungi, bacterial and fungal wilt organisms, and insects such as squash bugs can damage plant roots, stems, and vascular systems, limiting water uptake, and causing excess stress. However, there are many stresses that don’t involve diseases or insects. The following are some other causes of excess stress in vegetables this time of year.

Soil Compaction
Plants will have limited rooting in compacted areas and therefore cannot take up adequate water or mineral nutrients. In addition, compacted soils have reduced air exchange. Plants will often be stunted and will wilt early in the day in high temperatures. Cultivation can alleviate surface compaction but will be ineffective on deeper compaction.

High Soil Temperatures
Soils that have limited water holding capacity can have excessively high soil temperatures during long hot days in late spring and early summer. Late planted crops on black plastic mulch are very likely to be exposed to high soil temperatures and surface roots will often be damaged. Overhead irrigation over the black plastic mulch is very beneficial to reduce heat loads until plants have sufficient canopies to shade over the mulch.

Drip Tape and Drip Irrigation “Diseases”
Issues with drip irrigation can often be the cause of plant stress due to inadequate water. This includes plugged emitters; leaks due to insect or animal chewing that limit water flow further down the tape; leaky connections reducing flow; tape twisting and binding, again limiting flow past the point of the bind,; improper tape selection or improper irrigation timing leading to under application of water; limited well capacity also leading to under application of water; too wide of emitter spacing for the crop or soil; too wide of bed for a single tape (with double rows) and others drip irrigation problems. Over application of water in drip irrigation also can be an issue, especially in lower field areas and where soil types change in the field. This can lead to saturated beds limiting oxygen for roots. The keys to avoiding drip irrigation associated problems is to monitor fields closely, note any areas that look stressed, and investigate whether or not the drip irrigation is functioning properly. Soil moisture monitoring devices can aid greatly in detecting problems.

Inadequate Overhead Irrigation
Under-watering can lead to additional plant stress. Plugged nozzles are a major problem that often goes uncorrected. Excessive runoff due to compacted soils can lead to reduced water intake.

Excessive Fertilization
Salt induced stress conditions can occur when excess fertilizer, manure, or high salt compost is applied or when high salt index fertilizer is applied too close to vegetable plants.

Stand Reduction in Lima Beans

Friday, June 24th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Recommendations are for a stand of 3 to 4 plants per foot of row for baby limas. However, each year there are some lima bean fields that end up with lower stands than expected due to soil crusting, planter malfunctions, seed quality issues, errors in setting planting rates, or other problems. I recently visited a field that was planted deeper than normal in wet soil. The soil was tight and seeds were having a hard time emerging. The only option was to rotary hoe the field. Stand reductions are expected in this situation.

Fortunately, lima beans compensate very well for stand loss by producing larger plants that can bear more pods. As long as there are not large gaps in rows without plants, there will be little effect on yield. In research at UD, stand reductions of 50% reduced yields by only 14% in baby lima beans.


Keeping it Level

Friday, June 24th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

May and early June planted lima bean fields are being cultivated at this time. As cultivation season progresses, lima bean growers are reminded that harvest recovery can be affected by cultivation practices. In research by Dr. Jim Glancy and Ed Kee, they found harvest losses as high as 25% when ridging was 3 inches or more. A large part of this was due to pods left on plants that could not be harvested. It is therefore important to have the most level conditions possible. Cultivating too deeply, at too fast of speeds, when fields are too wet, or in ways that create ridges and valleys in the field will reduce harvested yields. Excessive wheel tracking in fields for other operations such as sidedressing or spraying can also cause losses.


How High Heat Affects Vegetables and Other Crop Plants

Friday, June 17th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

The plant temperature at which tissue dies is around 115°F. Normally, plant temperature is just above air temperature. However, plant temperature can rise to a critical level under certain conditions.

Plants have 3 major ways in which they dissipate excess heat: 1) long-wave radiation, 2) heat convection into the air and 3) transpiration.

A critical factor is transpiration. If transpiration is interrupted by stomatal closure due to water stress, inadequate water uptake, injury, vascular system plugging or other factors, a major cooling mechanism is lost. Without transpiration, the only way that plants can lose heat is by heat radiation back into the air or wind cooling. Under high temperatures, radiated heat builds up in the atmosphere around leaves, limiting further heat dissipation.

Dry soil conditions start a process that can also lead to excess heating in plants. In dry soils, roots produce Abscisic Acid (ABA). This is transported to leaves and signals to stomate guard cells to close. As stomates close, transpiration is reduced. Without water available for transpiration, plants cannot dissipate much of the heat in their tissues. This will cause internal leaf temperatures to rise.

Vegetables can dissipate a large amount of heat if they are functioning normally. However, in extreme temperatures (high 90s or 100s) there is a large increase the water vapor pressure deficient (dryness of the air). Rapid water loss from the plant in these conditions causes leaf stomates to close, again limiting cooling, and spiking leaf temperatures, potentially to critical levels causing damage or tissue death

Very hot, dry winds are a major factor in heat buildup in plants. This causes rapid water loss because leaves will be losing water more quickly than roots can take up water leading to heat injury. Therefore, heat damage is most prevalent in hot, sunny, windy days from 11 am to 4 pm when transpiration has been reduced. As the plants close stomates to reduce water loss, leaf temperatures will rise even more. In addition, wind can decrease leaf boundary layer resistance to water movement and cause quick dehydration. Wind can also carry large amounts of advected heat.

Photosynthesis rapidly decreases above 94°F so high temperatures will limit yields in many vegetables. While daytime temperatures can cause major heat related problems in plants, high night temperatures have great effects on vegetables, especially fruiting vegetables. The warmer the night temperature, the faster respiration processes. This limits the amount of sugars and other storage products that can go into fruits and developing seeds.

Heat injury in plants includes scalding and scorching of leaves and stems, sunburn on fruits and stems, leaf drop, rapid leaf death, and reduction in growth. Wilting is the major sign of water loss which can lead to heat damage. Plants often will drop leaves or in severe cases will “dry in place” where death is so rapid, abscission layers have not had time to form.

On black plastic mulch, surface temperatures can exceed 150°F. This heat can be radiated and reflected onto vegetables causing tremendous heat loading. This is particularly a problem in young plants that have limited shading of the plastic. This can cause heat lesions just above the plastic. Heat lesions are usually first seen on the south or south-west side of stems.

High heat and associated water uptake issues will cause heat stress problems. As heat stress becomes more severe this series of event occurs in plants:

1. decrease in photosynthesis

2. increased respiration

3. closing down of photosynthesis -closed stomates stops CO2 capture and increases photo-respiration

4. major slow-down in transpiration (cooling process loss and internal temperature increase)

5. cell membrane leakage (signals changes in protein synthesis)

6. continued physical water loss

7. growth inhibition

8. plant starvation through rapid use of food reserves, inefficient food use, and inability to call on reserves when and where needed

9. toxins generated through cell membrane releases and respiration problems

10. membrane integrity loss and protein breakdown

The major method to reduce heat stress is by overhead watering, sprinkling, and misting for improved water supply, reduction of tissue temperature, and lessening of the water vapor pressure deficit. Mulches can also help greatly. You can increase reflection and dissipation of radiative heat using reflective mulches or use low density, organic mulches such as straw to reduce surface radiation and conserve moisture.

In very hot areas of the world, shade cloth is used for partial shading to reduce advected heat and total incoming radiation. We will be demonstrating the use of shade cloth for summer production of day-neutral strawberries.

Much of this information was adapted from an article Heat Stress Syndrome by Kim D. Coder, Professor, Silvics/Ecology, Warnell School of Forest Resources, the University of Georgia