Posts Tagged ‘vegetable crop establishment’

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.


Managing Windbreaks in Vegetables

Friday, April 8th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Many vegetable growers plant windbreaks between areas where plastic mulch will be laid and vegetables will be transplanted. Windbreaks are often planted between every bed, every 2 or 3 beds, or in drive rows between groups of beds (4-8 beds). Windbreaks protect young transplants from wind damage and blowing sand and can help maintain higher bed temperatures by reducing heat losses from cold winds blowing over beds.

Most commonly rye is used because it is early and is tall compared to other small grains such as wheat or barley. There are several considerations when managing these rye windbreaks. In most cases the rye should be killed with a herbicide, most commonly paraquat, after it has reached full height. This is when the seed head has emerged. Consideration should be given to reduce the chance of seed formation which can become a weed issue in following crops (especially fall planted wheat or barley). When rye produces seed heads, and those seed heads begin to flower (pollen bearing anthers emerge from the seed head) and pollinate, there is about a 7-10 day period before viable seed is formed (seed is set). Burndown should occur before seed set.

If the field is to be followed with cover crop where there is no concern about the rye germinating in the field, then it can be allowed to go to maturity (normal between bed herbicide applications with shielded sprayers may still kill the rye before it reaches full maturity).

One issue with windbreaks is the movement of mites and insects out of the rye and onto the crop after it dies from burndown with a herbicide. Growers should be aware of this issue and plan for control measures during this burndown period if crops have already been planted. If windbreaks are allowed to mature naturally, this rapid outmovement of pests may be reduced initially but may be extended over a longer period.

For very early transplanted vegetables (April-early May) where rye windbreaks are between every 1-3 beds, the rye often is still elongating and may not have produce a seed head. In this situation, vegetables are transplanted before the rye is killed. The rye is managed with row middle herbicide treatments scheduled before vines start to run off of the plastic for vining crops such as watermelon or before staking for upright crops such as tomatoes. A shielded row middle sprayer is used and paraquat is added along with residual herbicide treatments.

For vegetables to be planted after rye has reached full height (May plantings), then a broadcast burndown with paraquat applied over plastic beds and windbreaks is often used. Transplating is delayed until a rain or irrigation has washed off the plastic. Do not use glyphosate for this type of burndown over plastic due the the potential for residuals washing into planting holes, affecting transplants

Where windbreaks are only in drive rows, then they should be killed before seed has set.

Early Sweet Corn

Friday, April 1st, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

The first early fresh market sweet corn plantings have been planted. This March planted corn most often is planted under vented clear plastic covers to provide for extra heat accumulation. This allows for harvest in June, several weeks ahead of field plantings. Another option to improve earliness is to seed through plastic mulch. Special wavelength selective mulch (IRT) will allow for more soil heating that black plastic, however the difference is not always enough to warrant the extra cost. Planting on IRT or black plastic mulch often gains 1-2 weeks. Early bare ground plantings using shorter season varieties can often make the 4th of July market. These are most successful on sandy soils that warm up more quickly. Some growers have had success with early plantings grown on ridges to speed warming even more. Bicolor varieties are often used for these early plantings due to their better cold tolerance.

Processors in the region are switching more acreage to supersweet production. They are also interested in planting as early in April that will still allow for good stands. Seed companies developing processing supersweet varieties have made great strides in improving cold tolerance for these early plantings. Company fieldmen also spend time working with seed companies to identify the highest vigor seed lots for planting early. Growers also have an important role to play in the success of early processing sweet corn plantings. Early plantings will require shallower seed depths and planters need to be adjusted so that seed is placed uniformly at the proper depth and so that there is good soil to seed contact. Fields that warm up quickly should be selected for early plantings and should be worked well ahead of time. Remember that the wetter a soil is, the longer it will take to warm up. If at all possible, plant on a warming trend. Soil temperature around the seed should be >60°F during the day for best germination.

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.

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.

Vegetable Double Cropping

Friday, July 2nd, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

I have been asked several times in the last two weeks about double cropping vegetables. The following are some considerations in double cropping.

Crop residue management is critical in order to get a good seed bed for the double crop vegetable. Make efforts to spread and incorporate residue evenly. Heavy areas of incorporated straw or vine will lead to crop variability. Incorporation of high carbon materials such as small grain straw can lead temporary nitrogen deficiencies. Therefore, extra nitrogen fertilizer will be needed to speed decomposition of heavy straw residue. In contrast, green materials such as pea vines will not cause nitrogen tie-up and will rapidly decompose. It is advised to allow some time (minimum 5-7 days) for residue decomposition before planting the next crop.

Allelopathic responses (toxic reactions) in the double crop planting have been found in certain cases when planting has occurred immediately after incorporation of residues. One example has been with pea vines. Fresh pea residues have been shown to release pisatin, a chemical which can inhibit the germination and seedling growth of some seeds. Allowing residue to dry before incorporation, moldboard plowing fresh residue so it is out of the germination area, or waiting for a period of time to allow incorporated residue to decompose and the pisatin to break down before replanting (7 or more days) would reduce the risk of this allelopathic reaction affecting following double-cropped vegetables.

Pay close attention to herbicide plant back restrictions for vegetable double crops. Low rates (0.5-0.75 lbs) of atrazine are often used in sweet corn and this normally does not affect subsequent plantings. However, higher rates can damage the double crop planting. Mesotrione (Callisto, component of Lexar and Lumax) which is used in sweet corn has significant replant restrictions to many vegetables as do topramezone (Impact) and tembotrione (Laudis), also labeled for sweet corn. Command, Reflex, and Pursuit are examples of other common herbicides with significant plant back restrictions. Check the Delaware Commercial Vegetable Production Recommendations book and the specific herbicide labels for appropriate waiting periods and crops rotational restrictions.

Vegetable Replanting Decisions

Friday, June 11th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

One of the most difficult decisions that vegetable growers and advisors have to make is when to replant vegetables with stand problems. Often we have little research base to go on in regard to these decisions and it becomes more of an educated guess. I have heard many anecdotes of fields with reduced stands that have yielded well.

There are many reasons for reduced stands – insects, birds, planter problems, soil crusting, herbicide damage, and seed quality problems to name just a few. Before you even consider replanting, make sure that you diagnose correctly what caused the stand reduction. If the problem is repeated you will have lost money twice.

A replanted field should have a high probability of increased yield potential compared to the stand being replaced. That yield increase needs to cover the cost of replanting (seed, herbicides, additional fertilizer, tillage, equipment costs, etc.) and any other opportunity costs such as lost potential for double cropping. Consider issues such as increased pesticide needs in later plantings (replanted sweet corn will often require more sprays for insect control for example). With processing vegetables, you need to work closely with the processor to see if rescheduling is possible. They may have already filled later acres or be beyond their cutoff dates for that crop for example. With fresh market vegetables, consider how replanting will affect your markets and the prices that will be obtained for later crops versus a partial early crop.

A major difficulty is evaluating the yield potential of the existing stand. This is further complicated in processing vegetables that are once-over harvested where stand variability may lead to difficulty in scheduling for peak quality. Where research on replanting vegetables is available for this region, use that as a guide. Crop insurance providers often have access to information on replant yields and should be consulted where crops are insured.

Many crops compensate well for lower populations. Lima beans are a good example. Stand reductions as much as 50 % result in little relative yield loss in lima beans. In general, vining crops and indeterminate crops compensate well for reduced stands as do crops that branch strongly. Some leafy vegetables such as greens can also compensate for low stands by producing larger leaves. Bush type vegetables with limited branching, determinate types, and vegetables that produce one harvestable plant part per seed or transplant will be less able to compensate for stand reductions. Consider the variety also. For example, many sweet corn hybrids will produce a harvestable second ear at lower populations and thus will compensate for reduced stands.

Also consider the vegetable type. For example, supersweet sweet corn varieties have a wider harvest window than normal sugary types and therefore irregular corn stands with variability in maturity can still be harvested with not much tonnage loss. Consider how later replanted fields might be affected by heat or cold. Replanted snap beans exposed to summer heat will have reduced yields; in contrast, later planted lima beans may be exposed to cooler temperatures at flowering and have higher yield potentials.

There certainly will be times where replanting a vegetable field is necessary and replanting makes economic sense; however, more often than not you will make more money by taking the partial stand to harvest.

Sweet Corn Vigor

Thursday, May 20th, 2010

Gordon Johnson, Extension Fruit & Vegetable Specialist;

Each year we see sweet corn fields with stand and plant vigor issues, especially in early planted fields. There can be many causes for stand loss and weak seedlings: surface compaction and crusting, birds, soil insects, cold soils that delay emergence, soil diseases affecting seeds or seedlings, wet soils, fertilizer injury, deep planting, and herbicide injury are just a few examples.

When checking sweet corn fields with vigor and stand problems, it is important to dig up seeds and affected plants and examine the seed remnants, roots, and mesocotyl (stem that pushes the seed leaf to emerge above the ground). Corn seedling survival and early vigor is directly tied to a healthy seed kernel and mesocotyl from planting through the six leaf stage. Any damage to the seed or mesocotyl during this period can lead to stunted or weak seedlings, and in severe cases, seedling death. This is because the corn seedling depends 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. The seed kernel provides the means for early roots to grow and these food reserves are also mobilized and transported through the mesocotyl to grow the first stalk and leaf tissue. The mesocotyl also serves to transport water and mineral nutrients from the seedling roots.

Sweet corn is more susceptible stand loss and poor vigor problems than field corn because the seed has less food reserves. Shrunken types (supersweet and sugary enhanced varieties) have even less stored food than “normal” types and therefore are more susceptible to stand problems.

I have looked at sweet corn fields with stand loss and vigor problems (uneven growth) over the years. Often, when digging up the seedlings and examining the seed remnants and mesocotyls, the kernels will be disintegrated and there will be darkening at the mesocotyl attachment. This means that the seeds will have deteriorated prematurely and therefore the full content of the food reserves in the seed were not available for seedling development leading to the stand and vigor issues. The question that needs to be answered is what caused the seed to deteriorate prematurely?

The answer of course will change from field to field. 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. Fungicide seed treatments are critical to control these diseases. Problems occur where seed treatments are not adequate, where disease organisms are at very high levels, or where soil conditions are too cold and seeds remain in the soil for extended periods before germination and emergence. The risk of seeding infection increases as germination and emergence is extended and protecting seed treatments dissipate.

Cold stress and cold soils is a common stress factor leading to poor stands. Often growers are pushing the limits and are planting sweet corn too early. While field corn will start to germinate at 50°F, many types of sweet corn need much warmer soils. This is especially true of supersweets and other shrunken types which perform best at soil temperatures 65°F or higher. Sweet corn germinates best at soil temperatures above 68°F. When soil temperatures are below 55°F, germination is greatly extended. Food nutrients are mobilized in the seed but are not being utilized rapidly by the plant. The seed then becomes a perfect food source for many soil microorganisms.

Soil insects can cause seed deterioration by feeding on seed contents and causing entrance wounds for disease organisms. Seed corn maggots and wireworms can feed on the seed directly causing stand losses. Grubs feed on seedling roots causing stunting. Wireworms and certain grubs will also feed on the mesocotyl causing seedlings to collapse. Sweet corn that takes more than 10 days to emerge is at great risk of injury due to insects as seed treatments dissipate. In fields with heavy infestations of soil insects seed treatments may not be adequate. Addition of manures or other organic matter sources just prior to early plantings can lead to heavy seed corn maggot populations that overwhelm seed treatments.

Stand issues are often related to the inherent poor vigor of sweet corn. Work with seed suppliers to obtain their best lots for early plantings with the largest seed sizes. Obtain varieties that perform better under cold stress.

The University of Delaware has two separate trials of processing sweet corn varieties from several seed companies that were planted in both early (April) and later (May). Results from these trials will be available later this year for future planning.

Break in the Weather

Thursday, April 8th, 2010

Gordon Johnson, Extension Fruit & Vegetable Specialist;

March was a very poor month for early spring crops due to cool, wet conditions. In most areas there were only 3-6 days in March where soils were suitable for planting. This limited March plantings of peas, potatoes, cabbage, spinach, and other early season vegetables. With the break in the weather, unseasonably high temperatures, and wind, much drying has occurred allowing for land preparation and planting into good soil conditions. Pea and potato planting is progressing, plastic is being laid for early warm season vegetables, early sweet corn has been planted and the first sweet corn plantings have emerged.

With the warm temperatures, growers are reminded that the likelihood that we will see a return to cold weather and will see frost again in April is still very high. At Georgetown, our last frost in 2008 and 2009 was on April 17. This means that growers should wait until the last week in April for the first plantings of frost sensitive crops such as melons and tomatoes or be prepared to use row covers for frost protection on those crops if planting earlier. For most of Delaware, there is still a 60-70 % chance of a frost through the third week in April; however, the risk of a major freeze event from this point on is very small.

Pea Planting Season

Thursday, March 4th, 2010

Gordon Johnson, Extension Fruit & Vegetable Specialist;

Wet field conditions have delayed early pea plantings across the region in 2010. In wet years, many fields often get planted under conditions that are not favorable for good pea performance as processors try to keep to a schedule. Planting into damp, compacted soils will lead to poor root growth, increased root rots, stunted plants, and poor pea yields. While planting in soils with higher soil moisture than desired is often unavoidable, there are some decisions that you can make to increase the chance of success in these sub-optimum conditions

1) Pay close attention to field selection. Choose the best drained fields with little or no low spots. Choose fields with soil types that warm quickly (sandy loams, loamy sands).

2) Consider planting into fields that have residue from a previous crop.

Corn stubble is desirable in these conditions. While not ideal from a trash standpoint (pieces of cob or stalk can be a contaminant at harvest), stalk pieces in the soil helps to maintain drainage, reduce potential compaction, and keep roots aerated.

3) Reduce tillage trips across the field to the minimum necessary. Use equipment with the lightest “footprint” to reduce compaction (lighter tractors, lower pressure tires, etc.)

4) Pay attention to your seed quality and seed treatments. Use the highest quality seed for these plantings with maximum protection from seed treatments (fungicides and insecticides). Germination in cold, wet soils will be much slower and extended over a longer period and protection from seed treatments will be challenged. Handle seed gently to reduce damage (cracks in seed coats and splits).

5) Plant shallower than normal and reduce down pressure on drill press wheels (however, make sure that soil to seed contact is adequate).