Posts Tagged ‘vegetable crop establishment’

Poor Vigor in Later Plantings of Sweet Corn

Friday, June 15th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Each year we see sweet corn field fields with stand and plant vigor issues even in corn planted later in the season when soils were warm. There can be many causes for stand loss and weak seedlings: surface compaction and crusting, soil insects, soil diseases affecting seeds or seedlings, wet soils, fertilizer injury, deep planting, and herbicide injury are just a few examples.

Corn seedlings depend on the seed for food to grow for several weeks after emergence until sufficient leaf area has been produced and nodal roots have become established. Sweet corn is more susceptible stand loss and poor vigor problems than field corn because the seed has less food reserves. If you dig up low vigor seedlings and kernels are disintegrated and there is darkening at the mesocotyl attachment this means that the seeds deteriorated prematurely and the full content of the food reserves in the seed were not available for seedling development leading to the stand and vigor issues.

Seed deterioration and/or poor vigor seedlings can be due to diseases that cause seed rots, seedling blights and/or root rots. Fungal disease organisms such as Pythium, Fusarium, Rhizoctonia, Aspergillus, and Penicillium are common in soils and many can even be carried on seeds.

While most of these seed diseases are problems in cold and wet soils, Penicillium is a common problem in warmer soils. Penicillium can survive in the soil and can also be seed borne. Plants infected with Penicillium will be stunted and off-color and seeding roots and mesocotyls will show discoloration below ground. Blue-green mold may evident on or in the seed remnant.

Fungicide seed treatments are critical to control seedling diseases and a systemic fungicide such as difenoconazole (a component of Dividend Extreme) will be necessary for diseases such as Penicillium that can be seed borne.

Poor vigor can also result from poorer quality seed. Work with seed suppliers to obtain their best seed lots and the largest seed sizes. Avoid old seeds and obtain varieties that known for good seedling vigor.

Problems With Corn Seedlings This Year

Friday, June 1st, 2012

Nancy Gregory, Plant Diagnostician;

Uneven stands have been seen this spring in corn fields. Corn seedling issues have been attributed mostly to environmental conditions, including dry soil at planting, resulting in variable depth of seeds and uneven emergence. Our early May weather resulted in wet, cool soil conditions conducive for fungi that invade young seedling roots and mesocotyls. Stress brought on by recent hot weather has exacerbated stress on seedlings. A recent article from Purdue University highlighted some issues also seen in the Midwest that apply to corn in Delaware:

Poor Stands or Stand Loss Due to Poor Seed or Plant Quality

Thursday, May 24th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist;

As spring planting season continues at a rapid pace, there are more reports of poor stands or stand losses in vegetable crops. The culprits are often soil insects or diseases; however, poor quality seed or plants can also be a source of the problem. You will most commonly see problems with poor quality plants or seeds when there is a cold period right after planting.

As we progress into the warmer part of the planting season, it is often assumed that late spring and summer plantings will not have stand issues as soil temperatures are warm and seeds should germinate and emerge quickly and plants should root out quickly if there is adequate moisture. With seeds, this is not always the case, especially if seed lots are of low vigor. Signs of low vigor seed will be abnormal appearance in the bag (shrivelled, cracked, off color, misshapen), small seedlings that emerge late or do not emerge at all, abnormal growth (twisting, snaking, or corkscrewing), small shriveled cotyledons in beans, small or distorted true leaves, swollen or split hypocotyls or coleptiles, and bleached out seedlings. Another issue affecting seed germination and emergence would be uneven or inadequately applied seed treatments (fungicides and insecticides).

Seed companies do a very good job of producing quality seed and most seed is produced in drier areas where seed diseases are limited. Once seed is harvested it is conditioned, treated, packaged, and stored. As seed is distributed it often goes through several phases of where it is handled and stored in different environments. Larger lots may be broken in to smaller units and then repackaged by resellers. Once seed arrives at the grower it will be stored and handled again, finally making it to the planter. In each new storage and handling activity, there is potential to do damage to the seed. Rough handling, high temperatures, and high humidity are particularly damaging to seeds.

Poor quality plants can be due to diseases or other pest damage. There are however other causes of quality issues in plants such as being poorly hardened off, overwatered, stressed, over or under fertilized, overgrown or leggy, over mature, or root bound. Chemical phytotoxicity can be another problem. As with seeds, improper plant handing can lead to quality problems including overcrowding in greenhouse and holding areas, rough handing of trays, and storing in light limited conditions for extended periods. Breaking plant stems plants, especially those that with excessive growth, is a common problem in transplanting as is damage to roots when pulling plants out of trays.

When troubleshooting stand losses it is important to consider these issues affecting seed or plant quality.

Can Antitranspirants and Antidesiccants Improve Vegetable Transplant Survival?

Thursday, April 5th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Antitranspirants and antidesiccants are materials applied to plants to limit water loss. They have been used with some success in horticulture, especially in the ornamental industry. I was recently asked if they could be used to improve transplant survivability for vegetable crops. Research has shown some benefits, but results have been inconsistent.

Transplants most commonly desiccate when water loss exceeds water uptake. This commonly occurs in transplants because root systems are small, limiting uptake, and water loss in windy conditions or on hot days is high.

Remember that most water moves out of plants through regulated pores in the leaves called stomates. This is called transpiration. These openings have specialized cells that can open and close, depending on environmental conditions and plant internal signals. Controlling stomates and transpiration can reduce water loss and plant wilting.

Leaves also have waxy cuticles that limit non-stomatal water losses. However, in plants that have thin cuticles, in new leaves where cuticles are still forming, and under extreme drying conditions, such as high winds, water loss through the cuticle can be significant.

Antitranspirants/antidesiccants work in one of 5 ways:

1. Chemicals such as hexaoctadecanol, cetyl-alcohol and steryl-alcohol reduce transpiration by entering the leaf and forming a barrier from within to reduce transpiration loss of water.

2. Chemicals that are metabolic inhibitors such as PMA and DSA prevent stomatal opening.

3. The plant hormone abscisic acid (ABA) causes stomatal closure.

4. Wax and oil emulsions or chemical film materials such as di-1-p-Menthene prevent water loss by completely covering the leaf surface with a film. This limits losses through the epidermis and by covering part of the stomatal opening.

5. Reflective antitranspirants, most commoly clay based, reflect light energy thus reducing leaf heating and water losses. This is most useful for later plantings under heat load. It does not have much impact on wind desiccation.

Not all of these materials are registered for food crops so you need to read the label before using them on vegetables. The most commonly used with vegetables have been film coverings and reflective materials.

In addition to these materials, gels have been used to protect transplant roots. Transplants are dipped in the gels prior to planting and this can reduce root loss due to drying and thus improve the ability of transplant roots to survive, grow, and take up water.

In a 4 year trial with cantaloupes, researchers in Nebraska evaluated the effects of an antitranspirant (Folicote) sprayed on plants and a polyacrylamide gel root dip (SuperSorb) on early growth of transplanted muskmelon with or without windbreak protection. They found that “overall transplanting success and early growth were enhanced the most by wind protection, followed by the polyacrylamide gel root dip, and least by the antitranspirant foliar spray”.

Currently research is underway looking at the plant growth regulator ABA for height control of transplants and to improve early season survivability. It is being trialed in crops such as tomato and watermelon in several states. ABA is the plant hormone that controls stomates. Results have been encouraging and it may be labeled for this use in the future.

My base recommendation is that for maximum transplant survival you should produce compact, well hardened off transplants and provide wind protection at transplanting. Antitranspirants and antidesiccants are additional tools that can marginally improve transplant success.

Avoiding Failures with Early Planted Vegetables

Thursday, April 5th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist;

The mild weather has many growers eager to get an early start with summer vegetables. Early markets are often the most profitable with higher prices. However, growers should proceed with caution and realize that failures can occur if cold sensitive vegetables are planted when temperatures are sub-optimal. As we get back to more seasonable weather in April, there will be many nights ahead with temperatures in the 30s and frosts and freezes are still a concern.

Each vegetable crop has a minimal temperature at which growth will occur. Our summer vegetables such as tomatoes, peppers, cucumbers, watermelons, and squash simply do not grow if temperatures are in the 40s or 50s. Squash and cucumbers do not put on growth with temperatures below 60°F, cantaloupes, watermelons, tomatoes, peppers, and eggplants will not put on growth with temperatures below 65°F. If temperatures are below these minimums, plants will just “sit still” and will be at risk of cold injury, wind injury, and damage from early season insects and diseases. Cold soils will limit root growth, further placing plants at risk due to inadequate water uptake and the risk of desiccation. Excess cold can also stunt some summer vegetables so that they do not fully recover. This is especially true of cantaloupes.

When planting summer vegetables early, growers need to consider all the tools available to maximize heat accumulation and minimize heat loss. The following is a list of these tools:

  • · Use raised beds or ridges. Ridges that are oriented east-west with crops planted on the south side, will benefit from the additional heat accumulation from the increased solar radiation on that side. Sandy soils heat up quicker due to lower water content.
  • · Use planted windbreaks, most commonly rye, between beds or rows. Windbreaks reduce heat loss from cold winds and help to accumulate heat. Rye reaches full height by the end of April on most of Delmarva. Cold winds are the most damaging to summer crops. Sand blasting during dry wind storms can actually cut plants off at the soil level. Growers doing field plantings for early crops in unprotected areas should always use windbreaks.
  • · For direct seeded crops, choose cold tolerant varieties, plant shallower and into well drained soils, and choose protected fields for earliest plantings. Also till soils well ahead of plantings to allow for them to heat up. Plant as soon as soil temperatures are adequate for germination. Also choose seed that has high quality and performs well in a cold germination test.
  • · To warm the soil more quickly, use plastic mulches. Plastic mulches increase soil temperature and help hold heat during night periods. They can increase soil temperatures 5-20 F° depending on mulch color. In order of lowest to highest heat accumulation Black < Red < Blue < Olive/Brown < Clear in selecting mulches. Mulches should be laid tight on a firm moist bed that is clod free. This will allow for more effective heat transfer and accumulation. Loose plastic and cloddy soils will reduce plastic mulch benefits.
  • · Use clear poly plastic covers. Most commonly, these come with slits or perforations to vent excess heat. They can be placed over direct seeded or transplanted crops with wire hoop supports (low tunnels) or they can be placed over ridges with transplants or seeds planted in the depression between the ridges. Zip tunnels and vented systems, where clear plastic can be easily closed and opened, have also been used. High tunnels also use poly plastic for protection and heat accumulation. I will discuss high tunnel management further in additional articles.
  • · Use spun bond poly or woven poly floating row covers to insulate, frost protect, reduce wind, reduce heat loss from soils and beds, and accumulate some heat. They can be placed directly over low growing crops such as strawberries or can be used with wire supports for other crops. The insulation they provide can protect 2-8 F° depending on thickness. Usually a 0.9-1.2 oz. cover is used to provide protection but not limit light too much.
  • · For smaller plantings, use of additional heat sinks to absorb heat during the day and then release it at night can promote earliness. Heat collection devices are usually filled with water and may be clear or black plastic containers or tubes.

Combinations of these practices will provide greater cold protection, heat accumulation, and earliness. This could include plastic mulch + row cover, plastic mulch + clear row cover + floating row cover, plastic mulch + row cover + heat sink, plastic mulch + clear row cover + floating row cover + heat sink. Use of these combinations in a high tunnel will further enhance success with early planted summer vegetables.

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.

Summer Vegetable Plantings for Fall Harvest

Thursday, July 28th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Plantings for fall harvested vegetables are underway. Timing these plantings can be a challenge, especially where multiple harvests are needed. Plantings from mid-July through the end of August may be made, with cutoff dates depending on the crop, variety, and season extension methods such as row covers, low tunnels, and high tunnels.

These plantings can be divided into 2 groups: 1) warm season vegetables for harvest up to a killing frost and 2) cool season vegetables for extended harvest in the fall.

The three main factors influencing crop growth and performance in the fall are daylength, heat units, and frost or freeze events. A few days difference in planting date this time of year can make a big difference in days to maturity in the fall.

Warm season vegetables for fall harvest include snap beans, squash, and cucumbers. July plantings of sweet corn can also be successful to extend seasons for farm stands. Mid-July plantings of tomatoes and peppers also are made for late harvests, particularly in high tunnels.

Cool season vegetables for fall harvest include cabbage, broccoli, and cauliflower; the cole crop greens, kale and collards; mustard and turnip greens; turnips for roots; spinach; beets; lettuce; leeks; green onions; and radishes.

To extend harvest in the fall, successive plantings are an option. However, days between plantings will need to be compressed. One day difference in early August planting for a crop like beans can mean a difference of several days in harvest date.

Another option to extend harvest in the fall is with planting different maturing varieties at the same time. This is particularly successful with crops such as broccoli and cabbage where maturity differences of more than 30 days can be found between varieties.

Another way to get later harvests is by use of row covers or protecting structures. This can allow for more heat accumulation and will aid with protection against frost and freezes. Decisions on what type or combination of covers/protection to use and when to apply the protection will influence fall vegetable maturation and duration of harvest.

A final factor for summer planting for fall production is on planting cutoff dates. For example, a crop such as cucumber may produce well with an August 2 planting but poorly with an August 8 planting; broccoli has a wider planting window than cauliflower; turnip greens have a wider planting window than kale.

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.


Storing Vegetable Seed

Friday, May 6th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Vegetable growers and processors throughout the region have purchased seeds for this crop year. Many of those spring planted seeds are already in the ground or are growing in greenhouses. However, seed for successive plantings through the summer must be stored. Much harm can be done to seed viability through the storage period and germination can be greatly reduced.

Many smaller growers buy larger quantities than they can use in a season to get volume discounts and then save the seed for upcoming years. Again, how that seed is stored can greatly affect germination in coming years. The most detrimental storage condition for seeds is high temperature coupled with very high humidity (think Delmarva in the summer). Seeds that have picked up moisture from the air will lose viability quickly. For each 1% increase in seed moisture, seeds lose half of their storage life. For each 9º F increase in temperature, seeds lose half of their storage life.

Uninsulated metal buildings make poor summer storage whereas older wooden sheds and barns or concrete block buildings are better. Seeds also should be kept in the dark. Most seed packaging excludes light but opened seed bags or containers can be at greater risk.

The ideal would be a well insulated structure that is shaded and kept dark. Air conditioning and refrigeration may be a good answer in the short term, especially for smaller lots.

As a general rule of thumb the combination of temperature with relative humidity in storage should be less than 100 ( 50°F + 50% RH, 40°F + 60 % RH, etc.) for seed storage. The colder the storage, the higher the allowable humidity, the hotter the temperature, the lower the allowable humidity. However, for longer term storage, the temperature and relative humidity should be kept somewhat lower (40°F; 30 % RH for most seeds).

How about freezing seeds (for example, long-term germplasm collections are stored at 0ºF)? Freezing will work very well if seeds are dry. If they have picked up significant moisture, they can be damaged in the freezing process. Also, freezing and thawing cycles can be damaging to seeds so remove seeds to be used and place the remainder back in the freezer quickly.

Vegetable seed that come in sealed containers or packaging should not be opened until just ready for use. Seeds in bags should also not be opened until being used. Open bags should be completely planted unless sealed and placed back in proper storage.

Vegetable seeds also vary by type in their ability to store for extended periods. For example, onion seed has less than 1 year storage potential and should be bought new each year. Sweet corn also stores poorly over 1 year, as does spinach. Beans and peas are intermediate with 2 year storage potential and peppers are also in the 2 year range. Melon, cucumber, squash, and pumpkin seed, as well as cole crop seeds (cabbage, broccoli, cauliflower, kale, collards), tomatoes, and eggplants can be stored for 3 years.


No-Till and Strip-Till Fresh Market Vegetables

Friday, April 22nd, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Most fresh market vegetable crops are either grown under conventional tillage or plasticulture systems requiring significant tillage. From a soil health perspective organic matter is the driver for healthy soils and the more the soil is worked, the faster that organic matter is decomposed and lost from soils.

One solution for this dilemma is using no-till, where organic matter can be conserved or increased. The best success story with no-till vegetables has been with pumpkins, which are commonly direct seeded through a killed cover crop mulch (often hairy vetch or rye) or through crop residue (most commonly barley or wheat small grain stubble). The mulch provided keeps pumpkins off of the ground and has greatly reduced fruit diseases and improved quality. Other seeded crops such as sweet corn and snap beans have been successfully no-tilled in the region.

No-till also has been shown to work with transplanted crops. Systems were developed and tested for tomatoes on hairy vetch and for numerous crops transplanted through small grain cover from peppers to cantaloupes. There were several no-till transplanters developed and we tested one at UD back in the 1990s.

Incorporating leguminous cover crops into these systems can reduce nitrogen needs for the vegetable crop being grown. In the pumpkin no-till into hairy vetch system, typically no additional N will be needed.

There are several reasons why no-till has not been more widely adopted for vegetable crops. No-till vegetables cannot be grown for early crops which are often the most profitable, due to soil temperatures remaining cooler, longer. Establishment can be an issue, especially through thick cover crop mulches. Weeds are controlled partially by the mulches and herbicides can be used for residual control; however, weed escapes can be problematic because cultivation is not available as a tool. Certain pests such as slugs, mites, and several insects can be an issue in no-till. Drip irrigation is also more difficult to use in no-till.

An alternative that combines some of the benefits of no-till with conventional tillage is strip-till, where cover is maintained between rows and a 6-12 ft tilled strip is where vegetables are seeded or transplanted. Strips can be formed with narrow rotary cultivators or with strip till coulters. This allows for earlier crops and for better establishment. A subsoiler can be run in the strips to improve root development. Management of the strip area needs to be planned ahead of time so that cover crops do not get too large – strips are formed when cover crops are small. There is also potential to install drip irrigation in the strips. In a strip-till system weed management is critical and residual herbicides will be critical.

Research has shown that for many vegetables, yields in strip till and no-till are comparable or higher than similar season conventional or plasticulture production.

The following are some of the keys to success with no-till fresh market vegetables:

1) Well drained soils are best for no-till and strip-till.

2) Fields to be no-tilled or strip-tilled should have minimal weed seed banks and little or no perennial weed problems.

3) An effective cover crop is required for no-till and strip-till systems to work. The cover crop should produce enough biomass to cover the soil and provide mulch that limits light and weed germination. Winter cover crops that have worked well for vegetable no-till in our area are hairy vetch, crimson clover, rye, vetch-rye combination, ryegrass, and subterrenean clover. For late summer no-till vegetable crops, several of the millets have provided good cover.

4) The cover crop should be easy to kill by chemical or mechanical means and have little or no-regrowth potential. Proper timing of cover crop kill is necessary to avoid reseeding in no-till systems. For strip-till systems, strips need to be formed early in the growth stage of the cover.

5) Attention needs to be paid at planting in no-till systems to provide good soil-seed contact for direct seeding or root placement and firming for transplants.

6) Provision should be made for moving residual herbicides into the soil through the mulch cover. This may require overhead irrigation.

7) Provision should be made to manage weed escapes. This may require spot spraying or hand weeding.