Laboratory and field testing of fungicides for control of Ergot in wheat and rye

Abstract

This project investigated the opportunities for control of ergot infection in wheat and rye with new fungicides and other chemicals under laboratory, glasshouse and field conditions.

Methodology was standardised to include artificial inoculation with a spore suspension at ear emergence so that inoculated ears produced honeydew and hence inoculum for secondary infection. Laboratory and glasshouse experiments used artificial inoculation only.

Tests on agar showed that 23 of the 34 fungicides tested had at least some activity in vitro. Strobilurins were not effective on agar, but showed strong activity when mixed with spore suspensions prior to inoculation of wheat ears. In field screening tests of the materials screened on agar, no fungicides were effective against ergot and seven gave significant increases in the mean numbers and weights of ergots. Glasshouse tests where fungicides were painted onto ears at very large rates showed some useful activity but some treatments were phytotoxic and prevented grain formation. Other glasshouse tests failed to provide any evidence of vapour activity against ergot. A range of fungicides applied to glasshouse-grown plants at stem extension significantly decreased ergot. Sprays at GS 31 were significantly better than sprays at GS 33 but there were no benefits of such early timings in subsequent field experiments.

In individual field experiments, fungicide performance was variable with significant control being achieved only occasionally with azole products (e.g. bromuconazole, epoxiconazole, fluquinconazole and tebuconazole) in some experiments. A number of fungicides significantly increased the number and, especially, weight of ergots, and the greatest effects were from strobilurins. There were no benefits from including additional non-ionic wetter in spray solutions, of using an electrostatic sprayer, of increasing spray volumes, of increasing the dose of active ingredient to double rate or of two-spray programmes.

Studies on the movement of radio-labelled carbendazim, tebuconazole and epoxiconazole showed very limited movement of fungicides painted on the flag leaf, injected into the stem below the ear or applied to an absorbent collar placed around the stem below the ear. When fungicide moved to the ear this was mainly to the glumes rather than to the ovary.

Fungicide sprays are unlikely to provide commercially-acceptable levels of ergot control. In some cases, fungicides may even aggravate the problem. Control of ergot will therefore continue to rely on rotations and cultural control, and avoiding susceptible crops on high-risk sites.