Include Vegetable Support Netting in your plan to combat Phytopathogens.

Support Netting like HORTOMALLAS® are a great aid to farmers against phytopathogens.  The installation of a trellising system using the “double netting” method or a V shape or even the horizontal support offers great visible and immediate advantages such as reduced labor requirements for tutoring the plant fastening it with twist ties or clips, and that is an immediate saving!

The advantages of a double netting system do not end in the labor cost reductions: 

the hidden and perhaps more important results come from the reduction of the rate of virus disease transmission!  Phyto viruses are transmitt by aphids most of the time, but many times and too commonly horticulture workers will be themselves the vectors of transmission when working among plants and touching each plant especially when placing a tutoring clip or fastening the plant to the raffia cable.  Diseases are also bring and spread to plants from the simple act of a workers handling the tobacco from a cigarette!

Given these facts, avoiding as much as possible physical contact between a worker and the plants

Becomes of the utmost importance to reduce phytopathogens, so a system that allows the plant to self-tutor without the intervention of the hands of workers (which in most cases happens exactly when the plant is in its development stage) will have clear cultural advantages that turn into greater plant yield and reduced used of chemicals.  A netting system that “catches” the plant on both sides, sandwiching it and allowing it to grow thru the meshes that will then act as supports, reduces by a great deal transmission and spreading of pathogens.

This is how HORTOMALLAS® contributes to an improved phytosanitary condition and a reduction of the costs also the quantity of spraying agrochemicals!

Here are some articles on the subject:

Once a virus (or other phytopathogens) is established inside a greenhouse, rapid spread of the disease could occur due to many hands-on activities in greenhouse tomato production, and the nature of mechanical transmission of these concerned viruses and viroids   https://www.virologyj.com/content/12/1/5

infected weeds grown in or around the greenhouse, or from workers hands with contagion,  https://scholar.lib.vt.edu/theses/available/etd-03022007-150404/unrestricted/THE_THESIS_FOR_RACHEL_LOVEDAY_2_26_07.pdf

TMV is spread readily by touch. The virus can survive on clothing in bits of plant debris for about two years, and can easily enter a new plant from a brief contact with a worker’s contaminated hands or clothing. Tobacco products can carry the virus, also phytopathogens can survive on the hands for hours after touching the tobacco product. Ensure that workers do not carry or use tobacco products near the plants, and wash well (with soap to kill the virus) after using tobacco products. Ensure that workers wear clothing not contaminated with tomato, tobacco or other host-plant material. Exclude non-essential people from greenhouses also growing areas.

https://ipm.uconn.edu/documents/raw2/Mosaic%20Diseases%20of%20Tomatoes/Mosaic%20Diseases%20of%20Tomatoes.php?aid=40

Sanitation is critical to prevent plant diseases Part 2: Field sanitation

Good sanitation in the field will reduce pathogen inoculum in vegetable plants.

Zucchini yellow mosaic virus on leaves. Photo credit: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org

Sanitation is one of many tactics need for an effective disease management strategy in the greenhouse and field. Sanitation includes any practice that aims to prevent the spread of pathogens by removing diseased and asymptomatic infected tissue, as well as decontaminating tools, equipment and washing hands.

This article on phytopathogens will help you and your employees use good sanitation and reduce pathogen inoculum, also known as “seeds” of the pathogen. Consistent and effective sanitation greatly increases the chances of raising healthy plants.

Sanitation in the field

Field sanitation needs to take place before, during and after the growing season. Prior to planting, fine-tune your weed management plan. Many weeds are know reservoirs for plant pathogens also insects. By controlling weed populations in your fields, you can reduce pathogens and their vector populations.

Wash soil off of farm equipment, including brushing off soil particles from shoes. These practices are especially important to prevent movement of soilborne pathogens such Sclerotinia sclerotiorum (causal agent of White mold), Phytophthora capsici, Verticillium dalhiae and different species of Fusarium. A power washer is an important piece of equipment in the battle against these diseases. Plows, discs, cultivators and other pieces of equipment should be power wash between fields.

Avoid working fields when plants are wet. This practice minimizes bacterial spread from diseased plants to healthy ones. For example, this tactic is important for tomato bacterial diseases such as spot, speck and canker that can prove challenging to control once in the field.

Remove infected plants or plant parts. As soon as symptoms appear, collect, bag and destroy or pile diseased material away from fields. Removing infected fruit also plant debris from the field can reduce the amount of pathogen inoculum that could move into healthy plant parts. Cull piles should be place away from production fields also waterways and, if possible, covered with a plastic tarp to speed up microbial decomposition and minimize phytopathogens spores from escaping. Burn, chop and spread, or deep plow debris at the end of the season. The choice of practice depends on the specific disease that was present in the field the previous season.

At harvest, carefully pick only healthy produce and avoid any mechanical damage on the fruit or other plant parts harvested.

Damage such as small wounds or bruises can be the point of entrance for microorganism that can compromise fruit quality while in transit or storage (short or long term).

Clean tools during use, disinfecting knives, shears and other harvesting tools often.

To accomplish this, wash tools with soapy water also dip or wipe in 70 percent ethanol or other products. It is important to refresh sanitizing solutions as specified on the product label. Tool sanitation and hand-washing can help minimize plant-to-plant spread of diseases caused by several bacteria also viruses. Provide hand-washing stations equipped with clean water and soap.

During harvest, careful hand-washing is critical to minimize plant pathogen spread. For example, tobacco mosaic virus (TMV) can be transmitt to tomatoes and peppers if hand-washing is poor after smoking cigarettes.

This tobacco virus is very stable also can be present on dry tobacco in cigarettes.

Examples where sanitation can help break the disease cycle

*Click on the disease name and the link will direct you to additional information and/or pictures of symptoms.

Sanitation requires detail-oriented employees. Always inspect plant material prior to planting in the field. Plant material can carry diseases also insect pest, introducing them to clean and new fields. Instruct employees on how to recognize common disease symptoms also the pests. Scouting often and thoroughly is need to identify problems as early as possible. The more eyes available to look at your vegetables plants in the greenhouse and the field, the more chances issues can be identifi earlier.

Tomato mosaic, cucumber mosaic, also spotted wilt are incite by viruses. The tomato mosaic virus is very stable and can persist in dry contaminated soil, in infected tomato debris, on or in the seed coat. The phytopathogens are transmitt readily from plant to plant by mechanical means. This may simply involve picking up the virus while working with infected plant material, then inoculating healthy plants by rubbing or brushing against them with contaminated tools, clothing, or hands. Aphids are not vectors of the tomato mosaic virus, although certain chewing insects may transmit the pathogen.

The cucumber mosaic virus overwinters in perennial weeds and may be transmitt to healthy plants by aphid vectors (although tomatoes are not the preferred host of aphids) or by mechanical means.

The cucumber mosaic virus cannot withstand drying, or persist in the soil. It also is more difficult than tobacco mosaic to transmit mechanically. Thus, cucumber mosaic tends to progress more slowly than tobacco mosaic in a field or garden.

The spotted wilt virus is transmitt from plant to plant by several species of small insects called thrips.

Thrips are less than one-quarter inch in length, light green to brown, and are extremely difficult to find on the plants. Several weedy hosts and ornamental plants may serve as alternate hosts for the virus.

The most important virus diseases on tomatoes In North Carolina is tobacco mosaic virus (TMV), but other viruses and phytopathogens may cause significant losses.

There are many strains of TMV and a few which occur in North Carolina are very damaging. The common ones only cause a mild mosaic. TMV can survive many months outside a living plant or insect, on tools, greenhouse frames, sawdust, and in the soil; in dried leaves such as in cigarettes it can survive for many years. It is rarely transmitt by insects. It is easily spread by touch from diseased plants or from contaminate objects. TMV can be seed-borne; however, the magnitude of seed with virus in contaminated lots is usually under two percent, but with subsequent handling of plants all plants usually become infected before picking.

Management

Control of viruses on tomato is based on a total program all year. By following these procedures you will reduce virus diseases and losses in a tomato crop.

Obtain seed from reputable sources that have been fermented or treated with acid or bleach by the seedsman. If seed has not been treated, proceed as follows: Mix 2 pints of 5.25% sodium hypochlorite solution (household bleach eg. Clorox) in 8 pints of water. Wash one pound of cleaned, fresh or dry, tomato seed in one gallon of the mixture for 40 minutes. Provide gentle and continuous agitation. Remove seed and spread on paper to air dry promptly.

Prepare fresh bleach solution for each batch of seed. Caution and remarks: (1) Beginners should try this seed treatment on inexpensive seed prior to treating large lots. (2) Seed germination may be reduced with some lots of seed. (3) Research has shown that this seed treatment is enhanced by prewashing the seed for 15 minutes in a solution of trisodium phosphate (one ounce of TSP in two quarts of water). (4) Do not recontaminate the seed by placing in used containers etc.

Control aphids early in the season to reduce initial infection and spread.

It may be a good idea to spray weeds bordering the field with an aphicide prior to seeding or planting the field, and all annual weeds in the field should be destroy. Avoid planting tomatoes close to established cucumber, squash, potato, tobacco, and pepper fields. Greenhouses containing tomatoes should be border by at least 150 feet of turf or pavement.

Decontaminate stakes, tools, tables, etc. by: (1) heating or steaming at 300 degrees F for 30 minutes; (2) soaking 10 minutes in 1% formaldehyde or a 1:10 dilution of a 5.25% sodium hypochlorite (10% Clorox) solution, do not rinse; or (3) by washing (enough to clean) in detergent at the concentrations recommended for washing clothes or dishes. Keep all solutions fresh.

Spray the plant bed prior to pulling or handling plants (24 hours) with whole or skim milk at the rate of 0.5 gallon per 100 square feet of beds; thorough coverage of plants is important.

For tomato production, seed in individual pots (peat pots, etc.) and do not touch or handle plants prior to setting in the field or greenhouse. Discard pots with seedlings that show leaf twisting, mosaic, or unusual growth.

Do not touch other seedlings while discarding them to prevent phytopathogens from spreading.

Dip hands in milk while handling plants every 5 minutes (more often if different lots of plants are handle). Rubber gloves will protect hands.

Remove and destroy diseased plants early in the season. Do not touch healthy plants with the diseased plants when removing them.

Disinfest equipment, tools, and hands on a regular basis while pulling, pruning, trellising, harvesting, and spraying plants, and when moving from one row or area to another.

Destroy tomato plants in the bed, field, or greenhouse as soon as possible after harvest.

Rotate tomato crops with small grain, corn, or pasture. Avoid following tomato crops after crops of tobacco, pepper, eggplant, or cucurbits.

the slightest brush of clothing infected with TMV was sufficient to spread the virus to uninfected plants, according to a study by Losenge et al.

pollinators such as bumble bees used in the pollination of some greenhouse crops, like cucumbers and tomatoes, can spread TMV.

it is possible for one plant to spread TMV phytopathogens to a neighboring plant just by growing together as their leaves come in contact with one another.

tobacco products can carry the virus and using them without washing your hands afterwards can potentially spread TMV.

For that reason, do not use tobacco in the greenhouse or without washing your hands prior to handling plant material.

Spread

PepMV is transmitt mechanically, particularly by contact. PepMV phytopathogens appears to spread at a much faster rate than the other known potexviruses such as Tomato mosaic virus (ToMV) and Potato virus X (PVX). PepMV is readily transmitt by contaminated tools, workers’ hands and clothing. Direct plant-to-plant contact and propagation by grafting can also spread the virus. Recent studies, in 2007 and 2008, reveal that PepMV can also be transmitt by seeds obtain from infect tomato plants.

However, the rate of transmission of PepMV from seed to growing embryo is low (0.005 – 0.057%), depending on the harvest interval of seeds obtained from infected mother plants. A similar study in 2005 suggest that PepMV may be seed-borne, but it can only be detected in the seed coat and not in the embryo. A report from the Netherlands claims that PepMV can only be detected in poorly cleaned fresh seed also the virus was never detected in well clean seed. Its ability to spread through recirculating irrigation systems is unknown.

Control

Since PepMV is spread chiefly by contact, control strategies for PepMV are strictly focused on sanitation and overall biosecurity measures. Plant removal, restricted access to affected rows, sanitation of workers (particularly hands and clothing) and tools are all critical. Dipping hands and tools in skim milk prior to and after working with each plant has been reported to reduce transmission of the virus. For details on control measures, greenhouse sanitation also biosecurity please refer the factsheets on “Management of Pepino Mosaic Virus in Greenhouse Tomatoes”, “On-Farm and Greenhouse Sanitation and Disinfection Practices” and “Biosecurity Guidelines” respectively.

More than 80 aphid species (Insecta: Hemiptera: Aphidoidea), including Myzus persicae and Aphis gossypii, are capable of transmitting the virus in a nonpersistent, stylet-borne manner (Figure 10).

The nonpersistent relationship implies that the insect acquires the virus in short probes (generally less than 60 sec.) and retains the virus for short periods of time (a few minutes) and loses the virus due to normal feeding activities. This means that the insect would have to reacquire the virus again (become viruliferous) to be able to transmit again. In the case of snap bean, the most important aphid vectors are the soybean aphid (Aphis glycines, recently introduced into the US), the yellow clover aphid (Therioaphis trifolii) and less importantly, the pea aphid (Acyrthosiphon pisum).

The virus is rapidly acquired by all instars, generally within one minute of feeding, but their ability to transmit the virus declines and is lost within several hours.

Transmission efficiency varies with the aphid species, virus strains, host plant species, environmental conditions and time of the year. Experimentally, CMV is one of the phytopathogens easily transmitted mechanically, but efficiency is increased by addition of a reducing agent such as 10mM sodium sulfite to the buffer when preparing inoculum.

Experimental mechanical transmission involves grinding infected tissue in a buffer (typically in a mortar with a pestle); many viruses can remain infectious during this process by using a simple buffer to resist pH change and protect the virus particle. Some viruses, like CMV and Tomato spotted wilt virus, are less stable and more vulnerable to being degraded during this process. Addition of a reducing agent can help to stabilize the virus, thereby enhancing its ability to remain infectious for transmission. Since phytopathogens like CMV is not a stable virus like Tobacco mosaic virus, it is not likely to be transmitted by workers touching infected plants during normal field operations.

TMV is not vectored by aphids, thrips, or leafhoppers; TMV spreads very efficiently in plant sap. This virus is transmitted by tools and workers as well as plant to plant contact where there are wounds caused by handling or insects. TMV can also persist in tobacco products.

Cultural Controls & Prevention of Phytopathogens:

There is no cure or treatment for TMV.

• Discard infected plants also thoroughly disinfest growing areas.
• Avoid growing vegetable transplants also ornamental crops in the same greenhouse.
• Workers should wash their hands after using tobacco products.

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