GE HARMAN

Departments of Horticultural Sciences and Plant Pathology, Cornell University, and BioWorks Inc., Geneva, NY 14456, USA

Background and objectives
Plant disease control is dominated by an over-reliance on chemical pesticides in order to produce adequate food and fibre, and cosmetically pleasing produce and ornamentals, for an increasing world population. Since at least the 1930s, fungi in the genus Trichoderma have been known to possess ability to control plant pathogenic fungi. It has been the objective of this laboratory and, recently, the commercial company BioWorks, to produce biological control products for use in commercial agriculture and horticulture.

Results and conclusions
We produced strain 1295-22 of T. harzianum using protoplast fusion [1]. This strain possessed both strong abilities as a biocontrol agent against various pathogenic fungi and a high level of rhizosphere competence. This strain can be applied as a seed treatment, as an in-furrow drench or granule, or to plants in the greenhouse. We have found that this same strain also has abilities to control diseases of above-ground plant parts and that it can grow and persist on leaves, flowers and fruits. However, it is invisible and non-toxic to plants or animals, so it does not have cosmetic or toxic disadvantages.

One product is T-22TM Planter Box, which is a dust designed to be applied by the farmer at the time of planting. The product is usually applied over fungicide- or fungicide+insecticide-treated seeds or seed pieces. Chemical fungicides give good short-term protection of the seed, but are not effective after about 2 weeks. T-22, however, grows onto the roots and provides advantages for the life of the crop; thus the combination provides advantages not possible for either chemical or biological treatments alone. T-22 gives healthier and more robust roots. Better roots permit the crop to withstand stresses such as disease, drought or nitrogen deficits because crop roots occupy a greater soil volume. As a consequence, the treatment frequently provides a yield improvement, especially when crops are stressed (sub-optimal growing conditions). T-22 increases both yield and size of potatoes; where potato size reflects grade and price received by the farmer, an increased return to the grower of several hundred dollars per acre has been obtained. For all crops, average return to growers is several-fold the price of the product; for some crops such as potatoes noted above and silage corn ($4.00 per ha treatments results in $100-200 increased revenue) the return is excellent.

Another product that contains T-22 is RootShield^TM granules and drench for use in the greenhouse. The granular product is added to the planting mix and the drench is applied after seeding, or in the case of ornamentals, after roots form on cuttings. Under usual greenhouse conditions, one application of the biological usually is as effective as several applications of conventional fungicides. For vegetable crops, the colonized roots can result in better transplant survival, control of root diseases in the field such as Fusarium crown and root rot of tomato, and increased yields [2].

Control of foliar and fruit diseases is also being investigated. Spray applications of T-22 controlled foliar phases of Botrytis and have the ability to control powdery mildew as well. For strawberries, T-22 can be applied to flowers either by a spray or by bees that exit hives through a T-22 preparation [2]. Both methods result in control of the disease on the fruit; bee delivery is superior to spray applications and equivalent to the most effective fungicides. Spray applications are still in development, and US EPA registrations are pending for all uses and crops except bee delivery to strawberry. Registrations and sales in countries other than the USA are beginning.

References
1. Stasz TE, Harman GE, Weeden NF, 1988. Mycologia 80, 141-150.
2. Harman GE, Bjorkman T, 1998. Trichoderma and Gliocladium. In Harman GE, Kubicek CP, eds, Vol. 2. Taylor and Francis, London (in press).