The crop continues to progress quite well. Topping has begun on some farms. Recent rains and warmer weather have helped to push out the buds in the earlier plantings. Leaf counts of topped tobacco on some farms have been reported to be in the 18-19 range. Aphid pressure is beginning to increase in several fields. Hornworms are also being found in most fields. To date, there are no widespread problems being reported and there have been no reports of Blue Mold in Ontario.
Beginning last week, we started to see Potato Virus Y infected tobacco plants in certain fields. This is about 2 weeks later than the first reports in 2013, however, it is still earlier than when we typically see the first symptoms of the disease in late July/early August. For detailed information about PVY, please refer to the technical bulletin entitled “Tobacco Pests and Disorders in the Field – Potato Virus Y” posted in the plant protection section under the research heading of this website.
PVY infected tobacco plant.
Another issue being reported on some farms is Leaf Drop. This is where the midrib of the leaf breaks about 2.5 cm (1 in) from the stalk. Leaf Drop is often seen in the lower stalk positions, i.e. sands, seconds or thirds. Some varieties are more prone to this condition than others. In addition, stage of growth and environmental conditions are contributing factors. Leaf Drop tends to be greatest shortly after a rain or irrigation when the plant is close to the topping stage and conditions are hot and humid. High winds during the stage when the plant is vulnerable to Leaf Drop can increase leaf breakage.
Leaf Drop shown near bottom of plant.
Target Spot (Rhizoctonia leaf spot) is also being seen in some fields. Ideal conditions for this disease are extended periods of high humidity and temperatures in the 20-30°C range. Protected areas in fields tend to provide more favourable conditions for this disease. The lower plant leaves are more severely affected by Target Spot. Several lesions on a leaf can cause the leaf to breakdown prematurely. Further information about Target Spot and its control can be found in OMAFRA’s publications 842 and 843.
Target Spot
Weather Fleck has started to show up recently. This disorder is caused by certain oxidants in the air, mainly ozone, that cause spotting on leaves. Initially the spots are usually less than 4 mm in diameter, and are black or brown in appearance. With time, these spots can turn gray or white. If there are several spots on a leaf, the tissue between the spots can dry up and turn brown. Some varieties are more susceptible to Weather Fleck than others. Damage is typically greater if it is foggy or there is a rain or irrigation while ozone levels are high.
Leaf spots caused by ozone.
Post prepared and sent by Canadian Tobacco Research Foundation
Mailing Address: CTRF, P.O. Box 322, Tillsonburg, ON N4G 4H5
Telephone: 519-842-8997
Web Address: http://ctrf1.com