Organic Integrated Pest Management in High Tunnel Vegetable, Small Fruit, and Flower Production

Missouri

The anticipated pests of focus were aphids and thrips; neither appeared in sufficient numbers during the year to cause any problems on tomatoes, peppers, zucchini, or potatoes. An unanticipated problem with the cover crops was the favorable habitat they created for voles. Control of voles became time consuming with the need of baits and traps to keep their levels tolerable. The issue of vole control and their habitat was discussed in the March 2005 issue of Growing for Market.

Screening Results

1. Use of Econet B raised the air temperature about 5◦ F. While airflow is not reduced significantly, the screen reduces wind by 45%, thus reducing air movement in this passively vented situation. For crops enjoying warmer temperatures in the summer, like melons and tomatoes, this may be acceptable, but with crops like cucumbers, peppers and (most, if not all) salad crops, this would be problematic.

2. Tomato fruitworm damage was virtually eliminated in a screened tunnel where tomatoes were not cultivated the year before. In the tunnel where tomatoes were cultivated, fruitworm damage was just as significant (about 18%, see note below). While not conclusive, this lends credence to the suspicion that a protected environment can aide tomato fruitworm in successfully over wintering further north then they normally would survive. Tomato fruitworm moths were detected in traps set up at 5 points from south to north in Missouri about mid-May. Since fruitworm damage is often not noted until harvest approaches (harvest typically begins about mid-June), it is difficult to know if the caterpillars are from eggs laid by tomato fruitworm moths flying up from the south, or from moths that emerged from pupae in a high tunnel.

3. Presence of European corn borer (larvae) did not occur on the bell pepper fruit in screened or unscreened tunnels by September. The previous year this pest appeared beginning in August, which is typical of the pest moving from corn beginning to dry down.

4. Both striped and spotted cucumber beetles were able to slip through the screen, with the screen providing no reduction in cucumber beetle numbers. Smaller screen would be required. Typical window screen would be a readily available inexpensive source, but this would restrict airflow more significantly, and may not be compatible with summer temperatures and passive ventilation.

* A combination of the OMRI approved insecticides Pyganic 5.0 and Dipel (B.T.) applied weekly provided control of tomato fruitworm damage, taking about 3 weeks to provide good control (3% of marketable fruit damaged by the caterpillar). Without the insecticides 18% of the marketable fruit was damaged. Caterpillar damage was usually substantial enough for the fruit to be culled.

Kansas State University-Wichita

In 2005, small infestation of two spotted spider mites (TSM) and few aphids were detected under high tunnel. Infestation of TSM was first observed in early April on the weeds between strawberry beds under high tunnel. Fortunately, no TSM infestation on strawberry plants was observed. In addition to the TSM under high tunnel, several beneficial insects, such as Ladybug larvae, Tachinid flies and lacewings were seen under high tunnel which might have prevented TSM from attacking strawberry plants. Strawberry harvest of high tunnel plants started early March. Sweet Charlie flowered and produced earlier than Chandler. Plants were harvested every two to three days. The 2005 harvest data show no significant damage from TSM infestation inside the high tunnel or outside (field plots). As expected, preliminary results showed yield was much higher under the high tunnel compared with that of field plots, data are yet to be analyzed.

Kansas State University-Olathe

Cucumber

In 2005, spotted cucumber beetle pressure was high, resulting in the need for weekly insecticide spray during much of the production period. Plots were harvested thrice weekly from mid-July through mid August, resulting in an overall production of 12 lb no. 1 cucumbers/plant (14.5 lb total/plant). There were significant differences between organic and conventional production systems with the organic cucumbers having significantly lower no. 1 yield than conventional (9.2 lb/plant vs. 14.6 lb/plant). There were no significant differences in cucumber yield between the field and high tunnel plots, though there was a tendency to higher no. 1 yield in the high tunnels (11.5 lb/plant in field vs. 12.8 lb/plant in high tunnels). Percentage of no. 1 cucumbers was significantly higher in conventional plots than in organic (90.5% vs 75.2%), and was also higher in high tunnels than in the open field (86.3% vs 79.3%). While differences in yields cannot be attributed solely to pest control, there were noticeable differences in abundance of cucumber beetles between organic and conventional treatments, with the permethrin effecting much greater residual control than the pyrethrin. There was typically an abundance of pests in the organic plots within 24 hours of treatment, while conventional plots remained relatively pest free between weekly sprays.

In 2006, cucumber beetle pressure was lower, and fewer pesticide sprays were required. Plots were harvested through the month of July with an average overall production of 15.7 lb no 1/plant (19 lb total/plant. There were no significant differences effects of organic vs. conventional or high tunnel vs open field treatments on yield of no. 1 cucumbers, though there was a tendency to higher yield in organic plots (16.8 lb/plant vs. 14.7 lb/plant), and in high tunnels (16.3 lb/plant vs. 15.2 lb/plant). Total yield and fruit counts were significantly higher in organic plots than in conventional. Given the absence of pest pressure, greater yield in the organic plot was presumably due go better soil fertility in organic plots.

Eggplant

In 2005, pest pressure on eggplant plots (flea beetle) was relatively high resulting in the need for weekly insecticide spray during the early production period. As the season progressed, plants grew large and pest pressure declined. Plots were harvested twice or weekly from mid-July through early October resulting in a no. 1 yield of 5.8 lb/plant (9.4 lb/plant). There were significant differences between organic and conventional production systems with the organic eggplant having significantly lower no. 1 yield than conventional (2.1 lb/plant vs. 6.1 lb/plant). There were also significant differences in no. 1 cucumber yield between the field and high tunnel plots, (4.7 lb/plant in field vs. 5.54 lb/plant in high tunnels). Percentage of no. 1 eggplant was significantly higher in conventional plots than in organic (73.8% vs 67.9%), and was also higher in high tunnels than in the open field (79.7% vs 61.9%). While differences in yields cannot be attributed solely to pest control, there were noticeable differences in abundance of flea beetles and lace beetles between organic and conventional treatments, with the permethrin effecting much greater residual control than the pyrethrin. As the season progressed, the greater vigor and health of the conventional crops was notable resulting in the higher yields recorded.

In 2006, pest pressure was lower, and fewer pesticide sprays were required. Plots were harvested from mid-July through late-September with an average overall production of 8.0 lb no 1/plant (11.8 lb total/plant). There were no significant differences effects of organic vs. conventional on no. 1 or total yield, but the effect of high tunnel on yield was highly significant, with no. 1 yield of 11.5 lb/plant vs. 4.4 lb/plant in the open field. The percentage of number 1 yield in high tunnel plots was significantly higher (71.1% vs. 58.3%) than in the open field. In the absence of significant pest pressure, high tunnel yield may have benefitted from improved soil fertility in the protected environment.

Tomato

Arthropod pressure on tomatoes in the 2005 trials was low, with fruit worms readily controlled in both organic and conventional plots by spinosad formulations. The incidence of foliar fungal diseases was, however, high, particularly in field plots, and little effort was made to control disease through the use of fungicides. Plots were harvested once or twice weekly from late-July through early October, resulting in an overall production of 12.7 lb no. 1 tomatoes/plant (22.8 lb total/plant). There were not significant differences between organic and conventional production systems though there was a tendency to higher no. 1 yield in conventional (14.4 lb/plant vs. 10.9 lb/plant). There were highly significant differences in no. 1 tomato yield between the field and high tunnel plots (5.8 lb/plant in field vs. 19.5 lb/plant in high tunnels). The differences in yield between high tunnel and open field were almost entirely due to the heavy infection of foliar fungal disease which occurred in the open field, but which did not occur in the rain-sheltered tomato plants within the high tunnel.

In 2006, arthropod pressure was again not significant in the tomato trial. While less severe than in 2005, foliar fungal diseases were again present in the open field plots. Tomato plots were harvested weekly from mid-July through the end of August with an average overall production of 13.4 lb no 1/plant. There were no significant effect of organic vs. conventional management, but high tunnels again resulted in significantly higher no. 1 yield compared to the open field (14.7 lb/plant vs 12.1 lb/plant). In 2006, there was a significantly higher percentage of no. 1 fruit harvested from high tunnels than open field plots (44.1% vs. 36.8%). Percent marketable (no. 1 and no. 2) from high tunnels was also higher than from open field (91.3% vs 86.2%).

Discussion

Trial results varied somewhat from 2005 to 2006 for each of the warm-season crops in this study. In 2005, when insect pressure was high, the organic cucumber and eggplant crops were not protected by weekly spray with pyrethrin, whereas weekly sprays of permethrin provided superior control of the major pests – spotted cucumber beetle on cucumber, and flea beetle and lace bug on eggplant. As a result, yields in organic eggplant and cucumber were significantly lower than from conventional plots. In 2006, pest pressure was lower in cucumber and eggplant plots, so there were no benefits of conventional pest control, and yields were comparable, or superior in the organic plots, probably due to superior soil fertility. In the case of tomato, arthropod pests (tomato fruit worm) were controlled equally by the organic and conventional formulations used, and there were not striking differences between yields of organic and conventional treatments. Tomato and eggplant to a lesser extent benefited significantly from the high tunnel environment. In the case of tomato, this benefit was enormous, particularly when high levels of foliar fungal disease destroyed the crop in the open field.

Future research efforts should focus on evaluating the efficacy of alternatives such as screen for cucumber beetle control in organic cucumber crops. The benefits of high tunnels with respect to reduction of foliar fungal disease, while generally recognized, have not been documented well in the scientific literature. This report is a step on that direction. A manuscript from these trials is in preparation for submission to a peer reviewed journal.

University of Nebraska at Lincoln (2005):

The vegetation is largely weedy species such as plaintain, crabgrass, some bromegrass, dandelions, henbit, chickweed, foxtails, and lambsquarters with about 25% bare ground. The statistical design is a split-split plot with four replications. Preliminary analysis of the data is pending. We anticipate continuing the data collection in 2006.

A summary sheet was designed and the weekly totals entered by order under ‘Beneficials” or ‘Pests’.

Some of the problems encountered were:

1. Difficulty in identifying insects on the sticky trap where the adhesive obscures parts needed for identification. (Examples; antennae stuck to head so form not discernable; wings stuck together or to body as in Diptera vs. Hymenoptera).

2. Difficulty in determining whether similar species are beneficial or pests in look-alike groups.

3. Dirty traps (from soil and debris contamination after being put out) that make counting difficult and may enable insects to escape.

4. Un-represented or under-represented categories of insects that either don’t fly (caterpillars or other immatures) or are infrequent filers (stink bugs, ground beetles, grasshoppers, etc.).

5. Most types of insects captured on the sticky traps normally move by flying.

6. Climatic and physical conditions greatly affect the frequency of certain groups of insects. Examples: temperature, humidity, wind conditions, season (certain insects may only occur for a short period of time) and sky conditions (cloudy/sunny).

The 2005 HT project identifications were done on a predominantly insect Order basis with a small number of readily recognizable genera noted. This method has called attention to some potential problems with insect identifications and has provided a basis for determining protocols for future projects.

In 2006, sampling and data collection of insects inside and outside the high tunnels before and after mowing with yellow sticky traps continued on a weekly basis. Identification of insects is difficult due to the glue on the traps obscuring key details. Data is entered onto the spreadsheets. Pressure to remove dandelions, bindweeds, and other weeds resulted in the vegetation of the entire area being chemically killed, disked, and replaced with turf grasses. This confounds the data considerably but we are optimistic that some general trends in insect movement into the high tunnels may become evident when the data is analyzed.

Experiences with biological control of insect pests in the high tunnels through the release of predatory insects continued. On the flower crops, thrips and spidermites were the biggest problems, followed by aphids. Predatory mites, Amblyseius cucumeris, provided adequate control of thrips for the early spring crops in the high tunnels. Thrips damaged the white and yellow snapdragon flowers. No thrips damage was observed on red, orange, or purple snapdragon flowers. Release rates were roughly 1000 per 100 sq ft, considered a heavy release rate, due to the packet size from the supplier. The interior space of each of the six high tunnels is approximately 100 sq. ft.
Spidermites were controlled with the predatory mite, Phytoseiulus persimilis, released when spidermites became evident on the leaves. Phytoseiulus persimilis was released at a rate of roughly 300 per 100 sq. ft. with repeated applications made through the summer. Control varied from excellent to fair, depending on the crop and the specific high tunnel.

Green peach aphids, Myzus persicae, were controlled quite well with releases of the parasitic wasp, Aphidius colemani. Aphidius colemani did not control the milkweed aphid, Aphis nerii, but releases of the convergent ladybeetle, Hippodamia convergens, were very successful against this pest on ornamental Asclepia species in both the high tunnels and the field.

A quandry arises with the use of biocontrol insects when insect pests occur for which there are no biocontrols, e.g. cucumber beetles (Diabrotica spp.), bean leaf beetles, and sunflower stem clipping weevils, which were a major problem in late-season ornamental sunflower crops. Pyganic (pyrethrum) and neem oil were options considered but both are contact control agents that would adversely affect the adults and larvae of beneficial insects, released or native.

Overall, use of predatory insects has been encouraging for control of spidermites, thrips, and aphids. In the future, predatory insects will be released earlier in the season with sequential releases as thrips pressure builds from March through June. Use of beneficial insects will continue as the high tunnel crop production system transitions toward certified organic status.