Posts Tagged ‘plasticulture’

Strawberries, Row Covers & Freeze Protection

Friday, March 2nd, 2012

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

Row cover management in plasticulture strawberries has been difficult this year due to the mild winter. In normal winters, row covers applied in December serve as winter protection to limit stand losses, dessication damage, and low temperature damage to buds. While plants are in a dormant state or when buds are not yet active in strawberries, the buds can tolerate temperatures down to 10°F.

Removing row covers during warmer winter periods can help to delay bud activity and reduce susceptibility to later freezes. Replace row covers in times when freezes are expected. Highest yield potentials are usually obtained by uncovering and covering in the late winter and spring based on expected temperatures when compared to the practice of keeping row covers on continuously into the flowering stage.

Once buds have begun to emerge, even when tight, they can only tolerate temperatures down to 22°F. As they begin to open, the critical temperature for damage increases (popcorn stage 26°F, open blossom 30°F).

For growers that have not been taking row covers on and off and will be leaving them on until bloom, the potential for losses due to freeze events will be greater during March due to the increased bud activity. Prior to forecasted freeze events, check the plant bud stage, and apply additional freeze production to limit losses. This may include double covering with row covers (2 layers), or the use of low volume sprinklers through the night and into the morning as a frost protection over the row covers. Loss of buds or flowers due to freeze events will reduce yields and profits substantially. A single 1.2 ounce floating row cover will give about 4 degrees of protection.

Strawberry Planting Season

Friday, September 9th, 2011

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

Planting season is here for plasticulture strawberry systems. In our area, most strawberries are planted using plugs produced by rooting tips. While plugs are more forgiving than bare root plants, actions prior to planting and at planting still can affect future performance. The goal is to have quick, uniform rooting across all plants on the bed so that proper sized crowns are produced before going into winter.

The first key is to have a firm, high, uniform raised bed with black plastic mulch tight against the soil. This allows heat to transfer to the soil, warming the root zone, and promoting fall growth. Loose plastic will not do this.

Liming should be done ahead of time if necessary to raise pH and provide Ca and Mg if necessary. Base fertilizer should be applied to the bed before formation to provide necessary P and K and adequate but not excessive N for fall growth (60-75 lbs N is recommended at bedding).

Whether you are planting by hand using a dibber to make holes or are using a water wheel transplanter, uniform planting depth is critical. Workers placing plugs should be trained to place plants so that crowns are not buried or are not above soil level. If buried, crowns will be susceptible to rots and plants may die or be stunted. Buried buds may not be able to leaf out. If planted too shallow, plugs will be susceptible to drying out before being able to root. In addition, during planting, workers should not plant weak, diseased, or damaged plants

Water is also critical during establishment. While we are having a spell of rainy weather, you cannot always count on rain during the establishment period. Drip irrigation should be run to wet the bed. However, this is usually not enough. Plants should receive water at transplanting in the hole and should also be watered overhead during the establishment period for best results.

Planting date is critical for plasticulture systems. While row cover management can be used to control growth, planting at the proper date will make row cover management in the fall much simpler. The ideal planting window is the first half of September, prior to September 20, for most areas in our region. Strawberries planted in this window should produce adequate numbers of branch crowns in the fall period and can then be covered in late November or early December for winter protection.

Later plantings (after September 20) will require earlier row covering to trap some heat and put on adequate fall growth.

In high tunnels, the planting window in the fall will be wider because of the extra heat provided and later plantings can be successful. However, some earliness will be lost.

Mustard Seed Meal as a Chemical Fumigation Alternative

Thursday, August 4th, 2011

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

With September strawberry planting season approaching for the annual plasticulture system, growers will be preparing beds and fumigating in the next 2 weeks. While several chemical fumigants are registered for strawberries, new fumigant use restrictions will make their use more of a challenge. In addition, strawberry growers that are organic or are using high tunnels with limited rotation are looking for effective fumigation alternatives.

One natural fumigant alternative that has shown great promise is mustard seed meal. According to researchers Dean Kopsell and Carl E. Sams, “studies conducted at The University of Tennessee showed that mustard seed meal has extremely high concentrations of isothiocyanates (ITCs). The seed meal is also a fertilizer source of nitrogen and other nutrients. When incorporated into the soil, ITCs act as effective biofumigants, reducing populations of pathogenic fungal species (Sclerotium, Rhizoctonia, Phytophthora, and Pythium), nematodes, weeds, and certain insect species.” ITCs are the same compounds found in some commercial chemical fumigants.

Specific studies with strawberries showed yield increases of as much as 50% compared to untreated controls using mustard seed meal. Additional research is going on in the region (Virginia, Maryland, Delaware, and Pennsylvania) with this material.

For mustard seed meal to be effective as a fumigant it has to be thoroughly worked into the bed area and plastic layed immediately after incorporation. The bed must remain evenly moist so the meal can break down (dry pockets will have delayed break down and can cause problems later) so a moist soil is important. A waiting period of 20 days is advised similar to a commercial fumigant before planting.

Current supplies of mustard seed meal come from Tennessee and costs $1.00-1.20 per pound. Recommended rate is 1000 lbs per mulched acre.

Because mustard seed meal is a natural compound, fumigant restrictions do not apply. It is also OMRI certified for organic production.

Summer Vegetable Plantings for Fall Harvest

Thursday, July 28th, 2011

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

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.

Stress in Vegetables

Friday, July 15th, 2011

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

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.

Heat Damage to Vegetable Transplants

Friday, June 10th, 2011

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

Watch for heat damage in transplants on black plastic mulch planted recently. This is a common problem in later plantings of peppers and tomatoes in particular.

Vegetable transplants are exposed to high soil temperatures at the soil line around the transplant hole. I took soil surface temperatures in black, white and metalized plastic mulch in mid-afternoon this Thursday (June 9). The air temperature was 97ºF. In open planting holes at the soil line, the temperature was >130ºF in the black plastic mulch, near 120ºF in the white plastic, and less than 110ºF in the metalized (aluminum) mulch.

The stem tissue just at or above the level of the plastic will be killed at these high temperatures and the transplants will then collapse and die. Small transplants do not have the ability to dissipate heat around the stem as roots are not yet grown out into the soil and water uptake is limited. Another factor in heat damage is that there is little or no shading of the mulch with the leaves of small transplants.

In addition, high bed temperatures have the potential to damage roots.

There are a number of practices that can reduce heat damage in later planted vegetable transplants:

● Delay planting until a cold front goes through if possible.

● Use larger transplants with greater stem diameters and more leaves to shade.

● Make a larger planting hole, cutting or burning out the plastic.

● When transplanting into the plastic, make sure the stems of transplants do not touch the plastic once set.

● Water sufficiently in the hole to reduce heat load, the more water the better.

● Plant in the evening, once the plastic has cooled down, or in the very early morning.

● Switch to white or aluminized plastic mulch for later plantings. This will reduce the heat loading significantly.

● In smaller plantings you may paint the planting zone on the black plastic mulch white with latex paint and then plant through this white strip once dry. You can also mulch around the planting holes with wet straw to reduce heat loading.

● Use overhead irrigation after planting to keep the plastic cooler.

 

Early Transplanting of Warm Season Vegetables

Thursday, April 14th, 2011

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

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

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

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

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

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

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

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

 

Protecting Your Plasticulture Strawberry Investment

Friday, April 1st, 2011

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

Prior to the cold snap, flowering had begun in some plasticulture strawberry fields in the region. As cold weather returned last week, temperatures dropped into the mid to low 20s requiring that row covers go back on. As a reminder, as buds become active but before flowers open, strawberry buds can survive down to temperatures of 22-27ºF, depending on just how close they are to opening. As flowers open, strawberries can only tolerate drops in temperature down to 30ºF. Small green fruit can stand temperatures down to 28ºF. During flowering and fruiting be prepared to freeze protect using row covers and in very cold conditions, sprinklers. It is critical to monitor temperatures. Temperature recorders that can be placed at crown height under the row cover are wise investments to do this monitoring.

When using sprinklers for frost protection, they must be used correctly. The idea is to slowly build up ice over the period when temperatures are below freezing over the plant or row covers. As ice is formed, some heat is released to the plant surface and to the surrounding air, due to the heat of fusion. To do this, sprinklers must be turned on before temperatures are at 34-35ºF. Use low volume sprinklers and apply irrigation throughout the night, building ice all night. Continue into the morning until ice has melted. An application rate of 0.15 inch per hour with no wind will provide protection to 22ºF. At colder temperatures or higher wind speeds more water will be needed.

It is recommended that for protection against frost above freezing, use sprinklers or row covers alone, for freezing temperatures in the mid to high 20s use sprinklers or row covers alone, for temperatures in the low 20s or below, use both sprinklers and row covers. A combination of row covers and sprinklers has been shown to protect below 20ºF.

Growers are strongly advised to subscribe to a weather forecast service to alert them of potential freezes in order to make frost protection decisions.

As fields are uncovered again, finish any cleanup of dead plant material and apply additional disease, mite, and insect controls. Fertigate nitrogen through the drip system, if it has not already been applied and monitor N levels using petiole and leaf samples. Petiole nitrate-nitrogen levels can be a good way to monitor and adjust your N program. At green-up, petiole nitrate-N should be around 1000-1500 ppm. As growth takes off, petiole nitrate-N should rise to above 4000 ppm. Petiole nitrate-N should be at 3000 – 4000 ppm during the first 4 weeks of picking and then decline gradually to around 1000 ppm at the end of harvest.

For more information about monitoring plasticulture strawberry nutrition, go the North Carolina Department of Agriculture & Consumer Services Agronomic Division plant tissue analysis site http://www.ncagr.gov/agronomi/pdffiles/sberrypta.pdf.

Fall Plasticulture Strawberry Planting and Management

Friday, September 17th, 2010

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

Planting for plasticulture strawberries is progressing across Delmarva. Research has shown that planting should be completed by September 15 for the best chance at high yields. While this is certainly true where row covers are not placed until late fall, later plantings are still successful with the use of early placement of row covers. The goal is to have adequate development of branch crowns (4-5 for most varieties) by spring. For plantings that go in later in September, it will be necessary to place row covers much earlier in the fall to keep temperatures high enough to achieve adequate branch crown development; how early will largely depend on the weather. Certainly, if an extended cold period in October and November is expected, row covering is advised on late plantings. Be prepared however to remove covers during late “Indian Summer” hot periods. One advantage to these late plantings is reduced runner formation and corresponding reduced labor in removing runners.

Fertigating Drip Irrigated Vegetables

Thursday, June 17th, 2010

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

Fertigation is the term used when soluble fertilizer sources are delivered through the irrigation system to crops. Drip irrigation is an ideal means to fertigate and to deliver mineral nutrients to vegetables during the growing season. Nutrients are carried with the irrigation water right to the root zone where they can be efficiently taken up by vegetable plants.

There are several strategies for fertigating vegetable plants. One strategy is to split fertigation so that crop nutrient needs, after preplant fertilizers are accounted for, are delivered in 4-5 applications just prior to critical growth stages. For example, for fruiting vegetables, the first fertilizer application through the drip system would be done after planting when plants have become established, the next prior to rapid vegetative growth, the next at flowering or early fruit formation, and the last during fruit expansion. For crops that have long fruiting and harvest periods, an additional application would be made after first harvest to encourage continued production.

Other strategies use weekly applications or applications of fertilizers through the drip system every time the crop is irrigated. In these systems, smaller amounts of fertilizers are applied each time and rates are increased as plants get larger. This requires a somewhat higher level of management.

For general vegetable fertigation through the drip, a 1-1-1 N-P2O5-K2O ratio soluble fertilizer (such as 20-20-20) is recommended. Where phosphorus (P) levels are very high, lower P ratios are appropriate (such as a 21-5-20). In some vegetables, only nitrogen (N) sources will be needed if soil fertility (P and K) are high. Soluble potassium nitrate and calcium nitrate are often used in combination in crops such as tomatoes and plasticulture strawberries to provide N, K (potassium), and Ca (Calcium).

Fully soluble fertilizers must be used for fertigation. Those in dry form must be mixed with water until they fully dissolve to create a concentrated stock solution. Those already in liquid form should be checked to make sure there has been no salting out of nutrients during storage – if salting out has occurred, you will need to make sure the fertilizer re-dissolves by agitation prior to use. It is important to know how much fertilizer is contained in these liquid stock solutions to match to injection rates.

A good quality fertilizer injector matched to the flow rate of your drip system is important to deliver the fertilizer the length of each bed uniformly in the field. Run the drip system to fill the drip tubes and come to steady pressure, start injecting, and then continue injecting using an injection rate that matches the irrigation period. You may then run the irrigation for a short period after fertigation to flush the lines. It is important not to over-irrigate as nutrients may be moved out of the root zone (especially N). Fertigation rates should be base on a mulched acre – that is only the amount of ground covered by plastic mulch.

For more information on fertigation go to our Commercial Vegetable Production Recommendation guide http://ag.udel.edu/extension/vegprogram/pdf/CIrrigation.pdf starting on page C-5.