Organic Greenhouse Vegetable Production

   J.A. Miles and M.M. Peet
Department of Horticultural Science
North Carolina State University
Raleigh, N.C. 27695-7609

Abstract: In a series of 4 greenhouse experiments, organic procedures for greenhouse tomato production, including use of biocontrol organisms, are being developed and compared with: 1) conventional production practices and 2) conventional fertilization practices coupled with the use of reduced risk (biorational) pesticides and IPM. This report summarizes the results of the second of the four experiments, but includes some observations from all experiments undertaken thus far.

The main challenge with in developing organic fertilization practices has been maintaining even fertilization levels-adequate, but not so excessive as to burn the plants. Clogged emitters and settling out were also a problem when using some of the organic fertilizers tested.

All insect control methods (conventional pesticides, mycoinsecticides and parasitoid wasps) were effective in controlling whiteflies when implemented for the entire growing season. Our experience with this project suggests that all the systems tested can result in comparable yields of high-quality fruit, but futher work needs to be done on organic methods of transplant production and fertigation. Another area requiring further study is the relative economics of the 3 systems.

Keywords: tomato, biocontrol, organic fertilization, organic transplant production, silverleaf whiteflies, Eretmocerus californicus, Eretmocerus eremicus, Encarsia formosa, Beauvaria bassiana

Introduction

Production of greenhouse tomatoes is increasing dramatically throughout the US, but particularly in the Southwestern US[1]. Many of these greenhouse complexes consist of 100-acre ranges, which are adding on 20 or more acres a year. If the market for conventionally grown greenhouse tomatoes becomes saturated, greenhouse growers, especially small growers, may need to explore niche markets, such as organic certification, in order to sell at a profit. Few pesticides are approved for greenhouse production; so many tomato greenhouses are already virtually pesticide free, reducing the barriers to adopting organic practices.

The purpose of our research, which was funded by Southern Region IPM, is two-fold. One aspect is to develop an organic fertilization regime using soilless substrates. Soil-based organic regimes, such as those used for outdoor production, are not well adapted for greenhouse use because of the difficulty of controlling soil diseases. The other aspect is to study various biological methods for controlling silverleaf (Bemisia argentifolii) and greenhouse (Trialuerides vaporariorum) whiteflies. Silverleaf whiteflies, Bemisia argentifolii, feed on the phloem sap of many horticultural greenhouse crops, including tomatoes. This feeding can result in retarded plant growth and fruit development as well as unevenly ripened fruit and sooty mold deposits on the fruit surface. Furthermore, whiteflies are a vector for Gemini viruses, which cause mosaic diseases. If left unchecked, whitefly populations will escalate rapidly and can decimate an entire crop. Currently, there are very few effective chemicals registered for whitefly control in greenhouse tomatoes. Many growers have used biological control agents, such as the parasitoid wasp, Encarsia formosa, successfully to control greenhouse whiteflies, Trialueroides vaporariorum. Unfortunately, E. formosa has not been effective in controlling Bemisia spp., Thus we were interested in testing efficacy of a newly-available biocontrol, Eretmocerus eremicus, which has been reported to control both silverleaf and greenhouse whiteflies.

Materials and Methods

General: 'Grace' tomatoes were grown in three greenhouses in upright plastic bags utilizing three different growing methods: organic, conventional, and biorational (IPM and use of reduced-risk pesticides). There was one growing method treatment in each greenhouse for each growing season, and treatments were rotated to different greenhouses between crops. All inputs for the organic system were allowable according to the Carolina Farm Stewardship Materials List for organic certification and/or were approved by the Organic Material Review Institute (OMRI). By the end of the project, organic methods will have been compared to conventional and biorational methods in a total of two spring and two fall crops. Methods and results from the Spring 1998 season are not reported here, as the modifications implemented in Fall 1998 gave better results. Generally the procedures used in Fall 1998 in all the houses gave satisfactory results and only slight modifications were made for the spring 1999 season. Results from the Spring 1999 season are not included as that data is still being collected and analyzed.

Diseases: Diseases were controlled in each greenhouse using a variety of cultural practices. Before each crop, greenhouses were disinfected by spraying surfaces with a 5-10 percent solution of household bleach (hypochlorite). Irrigation systems were flushed out with a 5-10% bleach solution and then with clear water in between crops. In the organic greenhouse, a floor mat filled with a disinfectant solution was placed inside the door to prevent disease organisms from entering. Further disease prevention practices included the use of Grace, a powdery mildew resistant cultivar and computer control of the greenhouse environment. No diseases have been observed to date in the greenhouses

Substrates: The mixes used in Fall 1998 were as follows:

Organic Substrates:

1.      85 % Fafard’s Special Organic Mix[2]: Ingredients: Canadian sphagnum peat moss, vermiculite, perlite, gypsum, dolomitic lime, pine bark
15 % Vermicycle
J.H. Biotech[3] "Natural Wet" 2T. /gal.
10 lbs./cu. yd. dolomitic lime
2.5 lbs./cu.yd. each, blood meal, bone meal, and potassium sulfate

 2.  63% Scott's 366 (coir): coconut coir, vermiculite, and perlite
      22% pine bark
      15% Vermicycle brand worm composted swine waste
      10 lbs./cu. yd. dolomitic lime
      2.5 lbs./cu.yd. each Blood meal, bone meal, and potassium sulfate

Conventional and Biorational Substrates:

1.  50% Southland SI-1: Canadian sphagnum peat moss, perlite, and vermiculite 
50% processed pine bark

2.  Fafard’s 4-P (normal commercial blend)

Transplant Production: Transplants were grown at the NCSU Horticultural Field Laboratory. The organic transplants were grown in Fafard’s Special Organic Mix and fertilized with Magna Gro. The conventional and biorational transplants were grown in Southland’s SI-1 medium and were fertilized with a commercial 20-20-20 fertilizer. The transplants for this season grew more rapidly than was expected and the conventional and biorational transplants were more advanced than the organic transplants. Consequently, fertilization ceased for the conventional and biorational seedlings, ten days before transplant. The plants had developed to the point of flowers on the first clusters so these clusters and all the leaves beneath them were removed and the stems were buried deeply at transplanting.

Post-Planting Fertilization: Conventional and biorational post-transplant fertigation began two weeks after transplanting. The organic plants were fertilized once by hand at this time. Since the EC levels from pour-through measurements were still high in the organic methods greenhouse, post-transplant fertigation did not begin in the organic greenhouse until four weeks after transplanting.  At that time two different organic fertilizers were used: EarthJuice and Magna-Gro. Formulations were developed to approximate the concentrations of nutrients used in the conventional/biorational formulation. Fertilizers were applied with every watering, except in the organic house, where on weekends plants were fed only water to flush the emitter and drip lines. Mixes were as follows:

Organic:

1.      Earth Juice[4]: Formulated to make one gal. of stock injected at a ratio of 50:1

Grow - analysis 2-1-1  ingredients: bat guano, Norwegian Sea Kelp, natural sulfate of potash, feather meal, oat bran, blood meal, and steamed bone meal

Bloom - analysis 0-3-1 ingredients: bat guano, Chilean sea bird guano, Norwegian seas kelp, natural sulfate of potash, steamed bone meal, oat bran, and rock phosphate

Catalyst - analysis 0.03-0.01-0.10 ingredients: oat bran, kelp, wheat malt, molasses, and yeast

Stage 1: Transplanting to first fruit set

1 qt. Grow
1 qt. Catalyst
2 c. Bloom
1 1/2 c. 10% K2O

Stage 2: First fruit set to topping

1 qt. + 1 1/4 c. Grow
1 qt. + 1 1/4 c. Catalyst
1 1/4 c. Bloom
1 1/4 c. K2O
1/2 c. Microburst Three

Stage 3: Topping to end of crop

1 qt. + 3 c. Grow
1 qt. + 3 c. Catalyst
3/4 c. Bloom
2 1/4 c. K2O
1/2 c. MicroBurst Three

2.   Magna Gro[5]: formulated to make 1 gal. of stock injected at a ratio of 70:1

Hydroponic Base Mix (HBM) - analysis 2-3-6 ingredients: poultry compost tea, pasteurized blood meal, calcium phosphate, and seaweed. This also contains trace minerals with fermented molasses in the form of Zn SO4, Mg SO4, and Fe SO4.

19%N  from poultry compost tea and pasteurized blood meal

 K-9 - 9% K₂O from seaweed

Stage 1: Transplanting to first fruit set

1 qt. + 1/4 c. HBM
1/2 TBS. 19% N
1/4 c. 9% K2O (K-9)

Stage 2: Harvest to topping

1 qt. + 1/4 c. HBM
1/3 c.   19% N
1/4 c.    9% K₂0

Stage 3: Topping to end of crop

1 qt. + 1/4 c. HBM
1 c.  19% N
2 c.  9% K₂0

Conventional: Plants grown using biorational and conventional methods were fertigated using “Chem-Gro” fertilizers from HydroGardens and supplemented with Ca(NO3)2, CaCl2, KNO3, and MgSO4 so that N-P-K concentrations were 115 ppm N, 45 ppm P, 195 ppm K for stage 1, 125 ppm N, 45 ppm P, 195 ppm K for stage 2, and 165 ppm N, 45 ppm P, 310 ppm K for stage 3 of plant development.

Data Collection: Data was collected on plant development, whitefly populations, success of parasitism, yield, fruit quality, and nutrient status of tissue, substrates, and leachate,. Rate of plant development was measured by the number of days to first flower. Nutrient status was measured by: 1) weekly pour-throughs; 2) beginning and end of season substrate analyses; and 3) periodic leaf tissue analysis.

Biological Control: At the beginning of each experiment, yellow sticky traps were hung in all three greenhouses. When whitefly adults appeared on the traps, control measures commenced. The yellow sticky cards were removed from the organic methods greenhouse before the parasitoids were released, however. Since both Bemisia spp. and T. vaporariorum populations were present, both E. eremicus and E. formosa were released. E. eremicus were released by placing an equal amount of carrier (provided by Greenspot[6]) into distribution boxes that were hung in the upper 25% of each plant. E. formosa  were released by hanging the cards randomly throughout the greenhouse in the upper 25% of the plants. Malathion was applied on a regular spray schedule in the conventional practices treatment. BotaniGard, a wettable powder formulation of Beauvaria bassiana, was used in the biorational methods greenhouse. Sprays were applied four times in a five-week period. In all greenhouses, whitefly data was collected by examining leaflets from five plants under a 30x dissecting microscope to determine adult whitefly genus (Bemisia or Trialuerides), the number of immatures of each genus and the percentage and the type of parasitism, if any. Weekly samples were collected from 5 plants, chosen randomly throughout each greenhouse.

Results and Discussion

In the first season, yields were higher in the conventional and biorational treatments than in the organic house. Fruit quality (percentage marketable) was highest in the organic system. In fall 1998, however, all the organic treatments had higher yields than the conventional or biorational treatments, with the Magna Gro/ Fafard’s combination producing the highest total yields, and the Fafard’s 4-P medium in the conventional methods greenhouse producing the lowest total yields. The highest percentage of #1 tomatoes was produced by the Earth Juice/ Scott’s 366 combination while the lowest percentage of #1 fruit came from the conventional / Fafard’s 4-P treatment. Tissue analyses indicated that nitrogen levels were low in the conventional / Fafard’s treatment one month after transplanting, possibly accounting for the poor early growth of the plants in this treatment, which led to slow plant development and low harvest yields. Fafard’s 4-P has performed well in other situations, so it is not clear why problems were experienced in this crop.

The main factors decreasing marketable yield were blossom-end rot and fruit cracking. Blossom end rot appeared first and was most pronounced in the conventional methods greenhouse. Calcium chloride sprayed for control resulted in some leaf burn in this treatment. Fruit cracking was also more of a problem in the conventional and biorational methods greenhouses than in the organic greenhouse, reflecting a trend also seen in the first experient for high quality fruit in the organic greenhouse.

Potassium levels in the organically grown plants were low in both Earth Juice treatments and in both biorational treatments. They were deficient in both Magna Gro treatments. Growing media had no effect on this problem. Initially there was a problem with the Earth Juice fertilizer clogging the injector. This problem was addressed by laying a fountain pump sideways in the stock tank so that concentrate was continually being swirled at the bottom of the tank. Emitters were also checked regularly to detect clogging. In future experiments, a lower dilution ratio than 1:50 will be used, which should help reduce clogging problems.

Whitefly populations increased by the end of the growing season, but not to the extent that they did in the first growing season. At the end of the season, the number of adults on the sticky cards were still lowest in the conventional and highest in the biorational methods greenhouses. It was again difficult to determine parasitism in the organic methods greenhouse due to the appearance of banded-wing whiteflies, whose pupal stage very closely resembles that of silverleaf whiteflies that are parasitized by Eretmocerus. Although parasitism could not be documented visually, whitefly populations remained low in this greenhouse during the growing season and didn’t escalate until one month after the last release of parasitoids. The BotaniGard formulation of B. bassiana was also effective only as long as it was sprayed on a regular basis. Fruit skin quality was high, and no residue appeared on the leaves.

Conclusions and Lessons Learned to Date

The following represent some of our observations and concerns after 3 seasons of experimentation. Statements should not be construed as product recommendations or lack thereof. This project was not designed to test particular products, but rather to develop general guidelines for the use of organic substrates and fertilizers, mycoinsecticides and biocontrols. Recommendations on fertilizer use in particular, are still being revised. Our experience suggest that all three systems can result in comparable yields of high-quality fruit, but futher work needs to be done on organic methods of transplant production and fertigation. Another area requiring further study is the relative economics of the 3 systems, an area not addressed in this project.

There are a number of obstacles to using organic substrates and fertilizers. An initial obstacle was locating suppliers. We have put together an on-line directory of organic suppliers, some national, but most located in the Carolinas. This directory can be accessed by selecting the databases option on the Organic Farming Systems Website: www.ncsu.edu/sustainable_farming_systems/. Fishmeal products were unpleasant in the closed working environment of the greenhouse, and none were used after the first crop. One of the organic fertilizer settled out before injection and clogged emitters, but this was partially overcome by keeping the concentrate stirred, flushing out the irrigation lines weekly and checking emitters frequently for clogging. Other strategies to deal with the high particulate content could include using emitters with high flow rates, e.g. 2 gph instead of 0.5 gph, and lower dilution ratios in the injectors so the fertilizer solution would be less concentrated. We have not yet tested either of the latter 2 strategies, however. We were satisfied with the overall performance of both fertilizers but growers would need to experiment on their own with concentrations. Potassium levels in the leaves were lower than desirable in most of the experiments but this problem should be correctable with additional adjustment of fertilzer blends. This is fairly straightforward with the Magna-Gro fertilizers as most nutrients, including K, are available separately. As interest increases in organic certification, new products may also appear on the market. Another problem with both organic systems was with avoiding high pH levels in the substrate and leachate. Monitoring the leachate using the pour-through method was useful in tracking changes. It may be useful to substitute ingredients in the bag mixes that either lower, or at least do not raise, pH.

Some difficulties we experienced with developing an organic fertilization regime are common to all new growing situations. For example, transplant quality could have been improved in the first two experiments. No commercial organic transplant substrates or fertilizer formulations are available, so we used the same materials as in the mature crop, which were probably not optimal for seedlings. Again, new products may make it easier to produce healthy transplants. Another problem experienced in the first crop, in particular, was applying excess fertilizer to correct a nutrient deficiency, resulting in fertilizer burn. In subsequent crops, cycles of under and over fertilization have been avoided or at least minimized by daily or weekly injection of nutrient solution and monitoring of the leachate for EC and nutrient levels. 

Problems experienced in using the mycoinsecticides and biocontrols have mostly been overcome, but it was difficult to document the effectiveness of either the mycoinsecticides or biocontrols by any method other than counts of whitefly populations. Infection by B. bassiana and parasitism of immatures by E. eremicus or E. fomosa were rarely observed directly under 30X dissecting microscope. Only five leaves were examined however, to avoid removing too many parasitized pupae, and it was also difficult to find good images of the appearance of pupae of the three different types of whiteflies when parasited by the two different parasitoids. It is possible that too few plants were present to support biocontrol populations. The two Beauvaria bassiana formulations were not tested in the same season, so definitive conclusions cannot be drawn about their relative effectiveness. BotaniGard, which is a wettable powder, did not cause leaf or fruit damage and controlled whitefly populations as long as applications continued. We feel that the best strategy with whiteflies is to prevent entry with insect screens and double entry doors, to monitor carefully with yellow sticky traps and begin control measures immediately after whiteflies are detected and continue them until the end of the crop.

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