University of Maryland Extension

Using Beauveria bassiana in High Tunnel Pest Management

Author: 
Dr. Gerald Brust - IPM Vegetable Specialist

2007

Summary: In 2007 we undertook a limited number of trials in HTs using the biopesticide-Beauveria bassiana, (Naturalis L) ATCC strain and (BotaniGard) GHA strain, alone and in combination with an Azadirachtin (Azadirect, a neem concentrate) drench of plants with applications of diatomaceous earth. Azadirect did not have much of an effect alone or in combination with any other treatment and because of its expense we decided it would not be used in future studies. B. bassiana ATCC strain worked well in the early part of the season (when it was cooler), but less well as it became warmer. However, B bassiana GHA strain worked much better in the warmer periods than the ATCC strain. B bassiana also seemed to work better when combined with diatomaceous earth (DE). What we think is occurring with the interaction of B. bassiana and DE is that the diatomaceous earth is causing tiny pin-pricks in the cuticle of the aphids and mites which allows the B. bassiana fungus a place to enter and infect the pest. Worms were easily controlled in all HTs by using the new threshold and the organic insecticide Entrust. In one organic research HT we released two natural enemies over the course of the season in the hopes of controlling first aphids and then later in the season mites. Our preliminary work showed that B. bassiana can work with the aphid midge, Aphidoletes aphidimyza (i.e., midge continued to feed and reduce aphid numbers as B. bassiana ATCC was used) but did not work well with the mite predator Phytoseiulus persimilis (i.e., B. bassiana infected predatory nymphs and adults resulting in little biocontrol).

Introduction: Vegetable growers have needed new and alternative methods to bring more money into their operations without investing much capital. The use of a high tunnel (HT) has worked well for many growers, but especially small farms to increase on-farm profits. Because HTs extend the vegetable growing season growers are able to supply customers with high quality fresh produce earlier and later into the spring and fall then is normally possible. Although HTs are relatively inexpensive to construct and use there is an increase in the amount of management that goes into their operation. There are few guidelines available for growers to use regarding how to manage their insect problems because so little is known about how best to manage pests in HTs.

Results:B bassiana reduced twospotted spider mites, Tetranychus urticae (Figs.1&2) and green peach aphids Myzus persicae (Figs.3&4) by an average of 83% compared with other organic insecticides or the control. Some strains of B. bassiana worked better than others when the temperature began to rise in the HTs. B. bassiana strain GHA worked better in controlling aphids and mites than did strain ATCC in August as compared with April. Using Azadirachtin alone or in combination with B. bassiana did not increase the control of aphids or mites as compared to using B bassiana alone. Because of its expense Azadirachtin does not appear to be a cost effective method of control for aphids and mites at this time. Diatomaceous earth alone did not significantly reduce aphid or mite populations, but when combined with B bassiana did an excellent job of aphid and mite control (Figs.1, 2, 3 and 4).

In one HT we examined the use of biocontrols (aphid midge,Aphidoletes aphidimyza and the mite predator Phytoseiulus persimilis) and their compatibility with B. bassiana. After several releases throughout May of the aphid midge and several applications of B. bassiana we were able to recover aphid midge larvae from aphid infested leaves (Figs.5&6). Even weeks after 98% of the aphid population was killed we still found midges on a few leaves. The predatory mite did not do as well. After several releases and applications of B. bassiana in August we could rarely find any Phytoseiulus persimilis on treated leaves. We were, however, able to find the mite predator to some extent on non treated mite-infested leaves.

Yields of tomatoes were usually not significantly different from one another between any of the treatments and varied to a great extent between HTs. One variety of tomato, MountainFresh+ was compared among the HTs to try and reduce variability (Fig. 7). There was a trend for Bb GHA strain to have greater yields compared with most of the other treatments. The control and DE treatments had significantly (p<0.05, orthogonal contrasts, SAS, 2008) more culls than the other treatments. Treatments GHA alone and GHA with Azadirect had the lowest number of culls of any treatment.

Figures 1 and 2 comparison of two strains of B. bassiana and other organic treatments - mite populations in April and August 2007

Figs. 3 & 4 Comparison of 2 strains of B. bassiana & other organic treatments in the control of green aphids

Figs. 5 and 6 # Aphid midge numbers per leaf

Fig. 7 Average total tomato yield by Sept. 15 from 4 HTs with 9-different treatments

Figs 8 and 9. Aphid and a Western flower thrips infected with B. bassiana strain GHA

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