Note to readers, attached is the complete final report for FNE97-177
Mr. Macfarlane has a small bog on which he grows cranberries organically. In a previous SARE project (FNE96-143) he experimented with non-chemical means of controlling cranberry fruitworm. Of the various measures he tried, only one– covering the plants with plastic row covers– appeared to have any appreciable effect, and this not for the reason postulated. His expectation of the row covers was that they would, by heating the soil underneath, promote early emergence of adult moths, which could then be caught on sticky traps under the plastic. What he found was that the adults easily escaped through ventilation holes in the plastic, but that the females were apparently reluctant to return through the vents to deposit their eggs on the berries. Mr. Macfarlane thereupon applied for another SARE grant to examine more closely the effects of row covers. In this project he tried three treatments: 1) a spunbonded polypropylene cover fixed in place for the season, 2) a clear vented plastic cover likewise fixed in place, and 3) a polypropylene cover placed over the rows each evening, and removed each morning. This last treatment is feasible because the adults leave the bog each day, and only return at night to lay their eggs.
Mr. Macfarlane found that the permanent polypropylene row cover was virtually 100% effective at preventing loss to cranberry fruitworm. However, fruit set under this cover was poor, apparently because pollinators had difficulty getting to the flowers. Fruit rot in these locations was also a problem, probably because of the higher humidity.
Pollination was satisfactory under the vented plastic and loss to cranberry fruitworm there was negligible. However weed control became a serious problem in these rows. Mr. Macfarlane believes the weed competition in turn caused delayed maturity of the crop.
The most successful treatment by far was the one involving daily removal and re-emplacement of the row cover. Where this was done, loss to cranberry fruitworm was negligible, fruit set was satisfactory, rot was not a problem, and weed control was facilitated. The labor cost was substantial, but Mr. Macfarlane believes it may be possible to bring this down to a more reasonable level by covering larger areas, concentrating on only the most productive parts of the bog, or monitoring more closely the egg-laying behavior of the insect pest. He intends to continue experimenting along these lines on his own.