Posts Tagged ‘transplant production’

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

Thursday, May 24th, 2012

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

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.

Transplant Shock

Friday, May 11th, 2012

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

A number of watermelon fields have had issues with poor plant performance and plant losses after transplanting in the last 10 days. Transplant shock is most prevalent when there are cold, windy conditions after transplanting and when night temperatures drop below 50°F. Plant and planting conditions that increase the risk of plant shock include:

Poor hardening off. Plants that come directly out of greenhouses or that have just recently come out of houses are most at risk. A proper hardening off will include reducing fertilizer and water and exposing plants to outside conditions in a protected area. It takes a minimum of 5 days to harden off plants.

Different plant maturities. Younger plants are more susceptible to shock. In watermelons, pollenizers are often younger than seedless due to having more rapid growth. Pollenizers are often most susceptible to plant shock after transplanting.

Small root systems. Plants grown in small cell sizes have fewer roots and if rooting conditions after transplanting are not favorable, they will be at a higher risk of shock than plants with larger root systems.

Root bound plants. An opposite problem can occur where plants have been in trays too long and roots have become root bound. Root bound plants dry out more quickly and often do not send out new roots as quickly because many roots in the root ball have died or are growing in circles in the cell.

Root systems not fully formed. In cells of plant trays, if the plant has not produced sufficient roots, it will not pull out of the tray properly and roots will be damaged when extracting plants and plants will be more susceptible to shock.

Rough handling during transplanting. If transplant crews damage plants when pulling out of trays and when setting plants, there will be increased plant shock. This includes stem crushing or damaging roots when extracting plants.

Setting plants too low or too high. In the transplanting process, burying plants too deep where green stem or leaf tissue is below ground can lead to that tissue being exposed to rotting organisms. Conversely, if root systems exposed (set to high), they can dry out and cause plant loss.

Inadequate plant water. If there is inadequate water at transplanting, plants can dry out and losses can occur.

Too much fertilizer. Too much fertilizer in the transplant water or in beds near the plant can cause salt injury and plant losses.

Poor plant handling. Keeping plants in tight conditions such as plant trucks for long periods of time, in extreme heat conditions, or where they have no light for an extended period will weaken plants and when exposed to the direct sunlight after transplanting, losses can occur. Plants shipped in that have been in transit too long or where truck conditions were stressful (cold or hot) will have more risk of shock. Plants that have dried out before transplanting are also at risk.

Air Pollution Damage to Transplants in the Greenhouse

Thursday, May 3rd, 2012

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

We have recently seen air pollution damage to greenhouse transplants. This can occur where coal or wood burning stoves are used and exhaust escapes when loading, where temporary unvented heaters are used in greenhouses, where heat exchangers in vented heaters have cracks, where exhaust pipes are leaking, or where fumes from burn piles or other sources are drawn into houses.

In fuel combustion, noxious gases can be produced if combustion is not complete. This can include: ethylene, sulfur dioxide, nitrous oxide and carbon monoxide. Even a clean burning furnace can have problems in airtight plastic greenhouses in cold periods where heaters are in constant operation. The level of oxygen can be depleted over several hours of continuous heating thus starving the combustion process of adequate oxygen and contributing harmful gasses.

During the combustion process, sulfur in fuel sources is converted to sulfur dioxide. If this leaks into the greenhouse and combines with the moisture there, sulfuric acid is formed. Low levels of sulfur dioxide may result in flecking and premature leaf drop. Higher levels can cause severe leaf burn, especially on young leaves.

Ethylene is a clear, odorless gas is a byproduct of the combustion of fuels. Ethylene can be damaging at levels as low as 0.05 ppm and even short exposures can cause leaf distortion, abortion of flower buds, defoliation and chlorosis. For more information on ethylene in greenhouses see the past article by Jerry Brust titled ‘Greenhouse Air Pollution Caused by Ethylene’ in WCU 17:6.

Disinfecting Flats for Transplants

Thursday, May 3rd, 2012

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

We have seen some problems where excess bleach used for disinfecting greenhouse flats caused damage to transplants. The following is some information from the University of Massachusetts on using bleach for disinfecting flats: “When used properly, chlorine is an effective disinfectant and has been used for many years by growers. A solution of chlorine bleach and water is short-lived and the half-life (time required for 50 percent reduction in strength) of a chlorine solution is only two hours. After two hours, only one-half as much chlorine is present as was present at first. After four hours, only one-fourth is there, and so on. To ensure the effectiveness of chlorine solutions, it should be prepared fresh just before each use. The concentration normally used is one part of household bleach (5.25 percent sodium hypochlorite) to nine parts of water, giving a final strength of 0.5 percent. Chlorine is corrosive. Repeated use of chlorine solutions may be harmful to plastics or metals. Objects to be sanitized with chlorine require 30 minutes of soaking and then should be rinsed with water. Bleach should be used in a well-ventilated area. It should also be noted that bleach is phytotoxic to some plants.”

Do not use straight bleach for disinfecting flats. Bleach contains sodium and chloride. Excess chlorine can be toxic to some plants. With excess chlorine, plants may wilt when soil moisture seems adequate, foliage has an abnormal dark blue/green color and individual leaves are dull and leathery, with scorching on leaf edges and premature yellowing of the oldest leaves. Sodium toxicity is seen as marginal leaf burn on the oldest leaves.

Inspect Watermelon and Cantaloupe Transplants, New Bacterial Fruit Blotch Factsheet

Thursday, May 3rd, 2012

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

As watermelon and cantaloupe transplanting continues on Delmarva, growers are reminded to inspect plants before they are transplanted into the field for signs of disease including Bacterial Fruit Blotch, Gummy Stem Blight, and Angular Leaf Spot.

Kate Everts and Gordon Johnson have put together a new factsheet on Bacterial Fruit Blotch, which will be of interest to watermelon growers. It is available online here: http://agdev.anr.udel.edu/weeklycropupdate/wp-content/uploads/2012/05/BacterialFruitBlotchFactsheet.pdf

Understanding Seed Waivers and Seed Born Diseases

Thursday, April 26th, 2012

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

A number of vegetable diseases can be transmitted through infected seed. For this reason, seed companies have developed quality assurance programs based on testing a certain amount of seeds in each seed lot for specific diseases. This most often involves the seed company growing out plants from these test lots and having trained individuals inspect the plants for signs of the disease. If there are suspicious plants, they are then further tested in the laboratory to confirm the disease. Sometimes seeds are tested directly for the specific disease organism (bacteria, virus, fungus). Only seed lots that have no disease detected are sold. For watermelon and cantaloupes, seed lots are tested for bacterial fruit blotch and often for gummy stem blight.

Because of past liability issues, growers are required to sign waiver forms to purchase watermelon and cantaloupe seeds from most companies. While this is often thought by growers to be a routine annoyance to purchase seeds, it is important to read the waiver forms and understand their implications.

These waivers commonly spell out what diseases the company tests for. The waiver will often have information on the testing process for these diseases. There will also be information about the diseases that the grower should know and often there will be detailed descriptions of how the disease develops and how to identify the disease.

In all waivers, there will be an important statement emphasizing that that the grower accepts the risks associated with those diseases.

The waiver may also include information on risk of nonperformance, assumption of risk, disclaimers or limitation of warranties, limits of liability, limits on damages, how to file a claim, statute of limitations on claims, arbitration of seed disputes (required by some states), expected remedies, limit on sales or transfers of seed, and attorney’s fees.

Once a seed waiver is signed then the seed company is protected from liability and this will reduce the ability of a grower to receive compensation if a seed borne disease does appear.

All growers are encouraged to understand what seed borne diseases are common with the vegetable crops that they grow, whether or not seed is treated or tested to reduce the chance of disease occurring, how to identify specific seed borne diseases, and how to manage seed borne diseases if they do occur (in greenhouse transplants or field plantings).

Growers should also maintain close relationships with seed suppliers and contact them immediately if a seed borne disease is suspected.

Preventing Spread of Bacterial Fruit Blotch in Watermelon Transplants

Thursday, April 12th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Now that transplant production is in full swing, it is timely to review what we do and don’t know, about bacterial fruit blotch (BFB) of watermelon. BFB of watermelon is caused by the bacterium Acidovorax avenae subsp. citrulli. Warm, humid conditions in greenhouse transplant houses are highly favorable for the spread of disease and the development of BFB symptoms. Although the disease spreads quickly in the transplant houses, it often is not noticeable in the field until shortly before harvest. There, BFB is damaging because it causes large olive green to brown water-soaked lesions on fruit, making them unmarketable.

Symptoms of BFB on seedlings are water-soaked areas of the lower surface of the cotyledons and inconspicuous lesions on leaves. In the image below, the leaves were incubated and the lesions have progressed along the veins and are obvious. BFB lesions will become necrotic often with yellow halos. Lesions are frequently delimited by veins. Infected seedlings collapse and die. The pathogen also causes disease on muskmelon or cantaloupe, honeydew, and on squash and pumpkin.

There are many steps that can lower the risk of development and spread of BFB on watermelon in the transplant house. All seed in a commercial greenhouse should have been tested and found to have “no evidence” of the pathogen. Don’t grow experimental lots that were not tested in a commercial house. Remember too, that testing, and “no evidence” does not guarantee that BFB will not develop, it is one of many steps to reduce the risk of disease. Inspect seedlings beginning at cotyledon expansion and at frequent intervals afterward. If BFB is suspected, send plants to the University of Maryland or University of Delaware diagnostic lab, or the Lower Eastern Shore Research and Education Center, for identification. Destroy all trays with symptomatic plants and those within a five foot radius. Remove adjoining trays to a separate – isolated – area for observation. Monitor these isolated seedlings daily and destroy trays where symptoms develop. All plants in the greenhouse should be sprayed with copper such as Kocide or Nordox. The applications should continue until the plants are shipped or transplanted to the field.

All the greenhouse surfaces should be sterilized prior to the production cycle. A solution of one part of bleach to nine parts of water, or Greenshield or Physan can be used on implements or benches. Don’t reuse trays.

Additional good practices for greenhouse transplant producers are:
· Workers should wash their hands and use a shoe bath when entering the greenhouse to work.
· Minimize the number of people that enter the greenhouse.
· Eliminate all weeds in and around the house.
· Maintain low humidity in the greenhouse.
· Water plants at their base and avoid splash between plants.
· Keep greenhouse flaps closed if it is windy.
· Segregate seedlots and separate them from each other with a vertical plastic sheet to avoid spread by splash or in aerosols.

Bacterial fruit blotch symptoms after incubation. Note the range of symptoms from small lesions on the true leaves to advanced lesions on the cotyledons.

Some Transplant Problems Not Caused by Pests or Diseases

Thursday, April 12th, 2012

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

Each year there are some problems that arise with vegetable transplants. Often they are disease or insect related (damping off, thrips, viruses, bacterial diseases, etc). See past WCU articles for specifics on greenhouse pest issues on transplants. However, often transplant problems are not pest related, but are due to other causes.

Poor growth, yellow plants, or stunted plants are often due to issues with the greenhouse media. Greenhouse media manufacturers have good quality control measures in place but things can go wrong on occasion – inadequate mixing, critical components missing or in the wrong proportions (i.e. wetting agents, fertilizers, lime), or defective, poor quality components. Media can also be affected by poor storage and handling. Most commonly this occurs when it is stored outside and bales or bags get wet. In addition, media has a certain shelf life – old media often dries out and is hard to get rewetted.

When growers start filling trays, any media that does not handle well should be viewed as suspect and should not be used. Contact your supplier and have them inspect and run tests on the suspect media. Avoid using overly dry or caked media, media that is hard to loosen, media with a bad smell, water logged media or media that is hard to wet.

Most media (but not all) will come with a starter lime and fertilizer charge. The fertilizer is designed to give about 4 week of nutrients. If the fertilizer is missing or improperly mixed or in the wrong proportion, seeds will germinate but seedlings will not grow much and will remain stunted. In this case, liquid fertilizer applications will need to start early.

Peat based media are acidic in nature and we generally can grow at lower pHs than soil. Plants will perform well from 5.4 to 6.4. Lime is added to peat based media and reacts over time after first wetting so pH will rise over time. Above 6.4 we often see iron deficiencies in transplants. This also occurs if irrigation water is alkaline (has high carbonates) causing pH to rise too high over time.

In high pH situations, to get transplant growth back to normal, use an acidifying fertilizer (high ammonium content) for liquid feeds. Use of iron products, such as chelated iron, as a foliar application on transplants can help them to green up prior to the pH drop with the acid fertilizer. In severe cases with very high media pH, use of iron sulfate solutions may be needed to more rapidly drop the pH. Acid additions to greenhouse irrigation water may also be considered for where water is alkaline.

If lime is missing or inadequate, and pH is below 5.2, plants may have magnesium deficiencies or may have iron or manganese toxicities. This also occurs in media that has been saturated for long periods of time. To correct this situation apply a liquid lime solution to the media and water it in well.

A good publication on media pH management can be found at: http://www.greenhouse.cornell.edu/crops/factsheets/pHGreenhouseCrops.pdf

Media that does not wet properly may not have enough wetting agent or the wetting agent may have deteriorated. They will be difficult to water and will not hold water well thus stressing plants. Application of additional greenhouse grade wetting agent may be needed.

If the fertilizer charge is too high, or if too high of concentration of liquid fertilizer feed is used, or if incorporated slow release fertilizer “dumps” nutrients, high salt concentrations can build up and stunt or damage plants. Leaf edge burn, “plant burn”, or plant desiccation will be the symptoms. Test the media for electrical conductivity (EC) to see if salt levels are high. The acceptable EC will depend on the type of test used (saturated paste, pour through, 1:1, 1:2) so the interpretation from the lab will be important. If salts are high, then leaching the media with water will be required.

Poor transplant growth or transplant injury can also be caused by:

· Heater exhaust in the house caused by cracked heat exchanger, inadequate venting, use of non-vented heaters

· Phytotoxicity from applied pesticides

· Use of paints, solvents, wood treatments, or other volatiles inside the greenhouse

· Use of herbicides in the greenhouse or near greenhouse vents

· Low temperatures due to inadequate heater capacity or heater malfunction or excessively high temperatures due to inadequate exhaust fan capacity or fan malfunction

Watermelon Seedling Diseases in the Greenhouse

Thursday, April 5th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Bacterial fruit blotch (BFB)
BFB
of watermelon, which is caused by the bacterium Acidovorax avenae subsp. citrulli, produces large olive green to brown water-soaked lesions on fruit, making them unmarketable. Symptoms of BFB on seedlings are water-soaked areas of the lower surface of the cotyledons and inconspicuous lesions on leaves. BFB lesions will become necrotic often with yellow halos. Lesions are frequently delimited by veins. Infected seedlings collapse and die.

If the bacterium is present, conditions in greenhouse transplant houses are highly favorable for the development of BFB symptoms and the spread of disease. Good practices for greenhouse transplant production are to disinfect surfaces before planting (benches, walls, walkways, etc.). The seed source should have tested negative for the pathogen with a minimum assay number of 10,000 seeds. Clean transplant trays (disinfect trays if they will be reused) and new soil must be used. Destroy any volunteer seedlings and keep the area in and around the greenhouse weed free. Avoid overhead watering if at all possible, or water in the middle of the day so that the plants dry thoroughly before evening. The bacterium can spread on mist and aerosols, so keep relative humidity as low as possible through proper watering and good air circulation in the greenhouse. Separate different seedlots, to reduce lot-to-lot spread. If BFB is suspected, collect a sample and submit it to your Extension educator, or specialist. Destroy all trays with symptomatic plants. Remove adjoining trays to a separate – isolated – area for observation. Monitor these isolated seedlings daily and destroy trays where symptoms develop. The remaining trays should be sprayed with a labeled fungicide and the applications continued until the plants are transplanted to the field.

Olive green water-soaked lesion on watermelon fruit. (Image courtesy David B. Langston, University of Georgia, Bugwood.org)

An inconspicuous lesion of bacterial fruit blotch on a watermelon transplant.

Other Greenhouse Diseases:

Angular leaf spot, which also is a bacterial disease, looks similar to BFB. This “look-alike” disease occurred in Delmarva’s greenhouses several years ago. Symptoms are small dark brown irregular lesions on cotyledons or leaves. Angular leaf spot is favored by cool wet weather. Usually conditions after transplanting to the field do not favor angular leaf spot disease development.

The fungal diseases gummy stem blight, Alternaria leaf blight, anthracnose, and Fusarium wilt can also be introduced into the greenhouse on watermelon seed or through inoculum from a previous crop. Diseases that are transmitted on seed often are randomly located throughout the greenhouse. Initial infections will occur as ‘foci’ or clusters of diseased plants.

Gummy stem blight infected transplants occur as clusters in an area around the initial infected seedling (foci).

Although I have not seen Fusarium wilt infected transplants in local commercial greenhouses, it has occurred in other states. Symptoms are wilted seedlings that may remain green or become chlorotic (yellow). This disease is of special concern because new strains or races can be introduced into an area on seedlings grown from infested seed.

Bottom line: If the seedlings appear diseased, identification of the problem is critical. Do not ship any trays containing plants with disease symptoms.

Can Antitranspirants and Antidesiccants Improve Vegetable Transplant Survival?

Thursday, April 5th, 2012

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

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.