Other pests attack cabbage in a different way to diamond back moth (DBM). Whereas DBM generally start on the land perimeters and gradually infect the entire field, bollworms tend to attack individual plants throughout the land.
They lay single eggs near the edges of young leaves. After eating small holes in this region, they work under the protective leaves where they are more difficult to kill.
Bollworms will never eat the head without visible holes in the cover leaves. Kill it at this vulnerable stage with a suitable spray programme or by proper scouting for eggs or young larvae. The latter option saves money, but requires regular inspections. P heremone traps determine if bollworm moths are active.
This, unlike DBM, is a sporadic pest as moths are only active in certain conditions. Trapped moths indicate that eggs are being laid. number of moths caught could help determine the severity of the attack.
Organic growers, who are limited with effective spray options, can use more traps which will virtually eliminate the problem. growers may find the extra cost worthwhile.
Note, the African bollworm in some instances is still incorrectly referred to as the American bollworm. The moths are night fliers, about 2cm long, a yellowy orange colour with faint dark markings. Pheremone traps are species- specific, so the moths can be identified easily. traps are fitted with a female hormone and insecticide that lure male moths. are only active in warm weather. They don’t occur in frosty areas in winter, and become inactive in sub-tropical areas during winter for a shorter period.
Semi-loopers do similar damage to bollworm. They have light stripes down their sides and a looping way of walking. These are sporadic pests as they are well controlled by minute parasitic wasps. They are usually either absent or present in epidemic proportions.
Once spotted, contact a pesticide expert as some products that are effective for bollworms don’t work well on semi-loopers. The moths have an almost triangular, yellow-gold marking on each wing.
The cabbage webworm is another potentially destructive caterpillar. It is only active in hot conditions and attacks the lower midrib of leaves and growing points. bores down the stem from this point, rendering the plant useless. The caterpillars are a very pale colour with longitudinal faint brown strips. Mevinphos is effective for this pest. – Bill Kerr Contact Bill Kerr on (016) 366 0616. |fw