Integrated pest management combines biological, cultural, physical, and chemical tools in a way that minimizes economic, health, and environmental risks. It is a rational approach to disease control that considers all factors in the classic disease triangle: characteristics of the crop plant, the effects of the environment on disease, and characteristics of the plant parasite causing disease. IPM takes advantage of the biological resources available today that were not on the market ten years ago. Careful planning is the key to success, as are training the greenhouse staff in thorough record keeping and being aware every day of new disease symptoms. A pest problem may arise each year at about the same time, or in the same part of a greenhouse. If you are aware of these trends, you can have on hand the materials or products needed to control the problem. Or you can change the physical environment to prevent or delay the onset of disease. A grower following IPM principles may find new markets opening for his produce as people become better educated about the differences between conventional practices and IPM.
Pre-season: Disease prevention begins at clean-up from the last crop. Some fungal spores can survive for a year and the sclerotia or other dormant structures can last much longer. After carefully removing all plant debris and discarding strings, the greenhouse walls and floor should be disinfected. Ten percent Clorox is the traditional cleaning solution, but quaternary ammonium is another option. It is recommended for greenhouse use because it is labeled for control of algae, fungi, bacteria, and viruses. In addition, it is not corrosive, and it is inexpensive. Because residual ammonia leaves as a gas, there should be no harmful residue after ventilation. The greenhouse should be empty for at least two weeks before starting a new crop, allowing enough time for white flies, powdery mildew spores and other obligate parasites to die.
Transplant Production: Growing your own seedlings is the very best way to insure that your transplants are disease free and in good condition. An early start with strong plants can shorten the time until the first harvest. Begin by purchasing quality seed, hybrid disease resistant varieties, and plant about 20% extra so that you can select the most vigorous individual seedlings for transplanting. Use a clean soil mix specially prepared for starting seeds. There should be no other plants in the transplant greenhouse to harbor insects or diseases that can infect the young tomato plants. If you adhere closely to the standard horticultural recommendations for temperature, fertilizer, and spacing, your transplants should be as wide as they are tall. Because embryonic flowers are forming in the plants after they are four weeks old, it is essential to keep the temperature above 60 degrees. Cooler temperatures for more than a week can result in catfaced fruit.
Crop Production: In a log book, all maintenance procedures, maximum and minimum temperatures, plant growth stages, insect pests, and diseases symptoms should be entered on a daily basis. The irrigation frequency and fertilizer components should be noted whenever changes are made. Balanced nutrition is critical to both high fruit production and disease resistance. Most greenhouse tomato growers send either the spent fertilizer solution or foliage samples for analysis by a laboratory that is familiar with greenhouse tomato requirements. Water quality can have an effect on solubility of fertilizer salts, so it should be checked for carbonates and pH. If you have hard well water, it may be necessary to bring the pH down by adding acid. The components of the fertilizer should change with growth stage. It is very important to make sure that the plants are not receiving too much nitrogen. Some varieties are very sensitive to excess nitrogen, which reduces yield and causes the plants to be more susceptible to disease. For strong stems, the calcium and magnesium balance is important. Blossom end rot is due to a lack of calcium, and may occur if plants are allowed to wilt, since a dry root system cannot deliver the nutrient. Calcium chloride or calcium nitrate can be used as a spray (l% solution, no surfactant) to correct serious blossom end rot. Automatic controls for the irrigation lines are the best way to regulate the delivery of water and fertilizer, either on a timed system or with solar sensing.
Disease Management: Several tomato diseases can be prevented by the selection of resistant varieties. Tobacco mosaic virus, Cladosporium leaf mold, Fusarium crown and root rot, and Verticillium root rot are generally not problems when the new recommended varieties are grown. The Dutch seed companies usually ship bacteria-free seed, so if only those plants are grown in the greenhouse, bacterial speck, spot, and canker should not be serious problems. Removing any symptomatic plants quickly from the greenhouse by placing the plants in a plastic bag before carrying them out will prevent spread of bacteria by contact.
Grey mold and powdery mildew remain as fungal diseases of greenhouse tomato that are very difficult to control. Resistance to these two diseases has not been found, and these fungi can move into the greenhouse easily from the outside. Both pathogens can colonize many species of weeds, as well as horticultural crops, so it is extremely important to maintain a weed-free environment. Mineral oil sprays and formulations of sulfur will slow down powdery mildew (caused by Erysiphe sp.) if used frequently. Botrytis cinerea is the causal agent of grey mold. It can be controlled with low humidity, but that is hard to achieve in a plastic hoop house on a rainy day. Many growers install hot water lines below the tomato plants to dry the foliage. It is important to exchange warm, moist air with cool, dry outdoor air at least once a day, preferably about four p.m. so the plants will be drier at night. Roof vents or a small exhaust fan at the peak of the house can reduce the humidity dramatically. The fungicides registered for use on grey mold of greenhouse tomato in New York, Botran and Exotherm Termil, have only preventative action, not curative. At this time, it is not possible to control grey mold with pesticides alone; a cultural strategy is required. Deleafing is a standard practice to remove infected leaves and improve ventilation near the moist soil and floor. Reducing the plant population density in the Northeast can help control grey mold and increase yield, with the optimum spacing about 4 to 4.5 square feet per plant.
The greatest economic damage from grey mold happens when stem lesions kill the plants, causing the loss of many clusters of fruit. The infections begin on the leaves and flowers, the most susceptible tissues of the plants. Wounded leaves, leaves in the dark, moist interior of the canopy, and leaves with drops of moisture on them are the first ones infected. As leaves begin to senesce and turn yellow, the fungus begins to sporulate. The frequency of grey mold infections increases in dark, rainy weather when the greenhouse is closed and moist air is trapped inside. The fungus enters the stem easily by growing from an infected leaf up the petiole into the stem, often before sporulation begins. Frequent deleafing is the best way to protect the stem from gray mold infections.
Purpose: To test the efficacy of biological control products on disease, and determine any effects on yield. Research on new and experimental products took place in a large commercial operation and Station greenhouses, funded by SARE/ACE and NE IPM.
These products were compared to untreated controls and to plants sprayed with chlorothalonil (Bravo was used for local application instead of Exotherm Termil canisters) to determine if they had an effect on disease incidence or severity and on yield. Treatments were applied twice between March 19 and April 8 (seeds sown Jan. 2). Spraying ceased at fruit set to prevent cross contamination of the crop. Disease severity on the leaves was assessed each week for five weeks beginning in April. Very few infected leaves were observed until the third rating, April 22. The number of infected leaves was counted, and the percent leaf area infected was estimated. Tomato harvest began May 2l; tomatoes were picked three times a week for 1l weeks, each treatment and replication were weighed separately.
% leaf area
|Treatment Mean Yield (lb)||Number of Plants Surviving||Yield per Plant(lb)|
|control||4.4 b||74.6||6.9 c||10.2 bc|
|chlorothalonil||2.4 a||76.2||7.3 a||10.1 bc|
|Mycostop D||2.5a||84.6||6.6 d||12.1 a|
|Mycostop S||4.6 b||81.4||6.9 bc||11.0 ab|
|TopShield||3.4 ab||79.2||7.4 a||10.3 bc|
|Bac-Pack||4.4 b||84.7||7.2 ab||11.3 ab|
All three biological control products show promise in greenhouse tomato production. Mycostop reduced grey mold on leaves significantly compared to the control, and also increased yield by almost 2 pounds per plant, which more than pays for the use of the product. The next step in this project is to try combinations of these sprays and drenches to try to reduce disease, increase the number of plants remaining at the end of the season, and also increase per plant yield.
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