Dry Edible Beans: Other Crop Problems
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811: Agronomy Guide > Dry
Edible Beans > Other Crop Problems
Insects and Diseases
Figure 5-1, Dry Edible
Bean Scouting Calendar, shows insects, pests and diseases that
could be causing symptoms in the field. Individual descriptions
of insects, pests and diseases, scouting and management strategies
can be found in Chapter 13, Insects and
Pests of Field Crops, and Chapter 14,
Diseases of Field Crops.
Frost and Hail Damage
Both frost and hail can be devastating to a bean crop. The extent
of early-season frost damage will depend upon where the plants were
damaged. If the plant is damaged below the cotyledons, it will not
recover. If the growing point is damaged, but the lower stem remains
intact, the plant will send out new shoots from the base of the
leaves or cotyledons. Wait a few days before replanting to see if
these shoots appear.
Bronzing is not caused by a living organism or pathogen but instead is the result of ozone damage to the leaf surface. A reddish-brown flecking or "bronzing" occurs on the upper leaf surface (Plate 29). Affected leaves are often the highest leaves on the plant. Bronzing often occurs shortly following an ozone event. The number of leaves affected varies, depending on exposure duration. Symptoms may be more severe on plants under moist conditions. Under dry conditions, plants are more tolerant to ozone. The amount of damage found on the plant or in an area often corresponds to air pollution alerts or heavy thunderstorms. These conditions can result in atmospheric ozone being forced down onto the crop. Ozone is also produced when lightning strikes. The higher the concentration of ozone and the longer the duration, the greater the impact on the crop. Use tolerant varieties in areas that have a history of ozone events.
Seed Quality Problems
Poor seed quality reduces germination and vigour of seedlings. Mechanically damaged seed may cause bald-headed beans (beans that emerge, but have no growing point). This injury should not be confused with symptoms of seed corn maggots, which will leave the seedlings ragged in appearance. Poor-quality seed can also cause seedlings to have broken or cracked cotyledons, or hypocotyl. Damaged seedlings are more prone to diseases and insect damage. Plant only high-quality certified seed. Treat seed with a fungicide at planting to protect against seedling disease. Handle seed gently to minimize mechanical damage.
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