Various non-chemical methods, such as physical barriers, sanitation, and adjustment of planting dates, have been tried with limited success for control of the cabbage maggot, but few growers use such practices because of prohibitive costs or labor requirements. Entomopathogenic nematodes are an alternative that have potential for managing cabbage maggot at reasonable cost without excessive labor.
Recent research investigated the effectiveness of six species or strains of nematodes in both greenhouse experiments and in the field in New York. In potted cabbage plants, Steinernema feltiae (strain 27) was more effective in reducing the number of cabbage maggot larvae developing on the plants than S. feltiae (369 strain), S. carpocapsae (25 strain and NY001 strain), S. riobravis (355 strain), and Heterorahbditis bacteriophora (Oswego strain), so it was selected for use in the field experiments.
Nematode applications significantly reduced root injury to cabbage plants in the field. However, some portion of the cabbage maggot population escaped nematode attack. Soil surface applications were more effective than subsurface applications in preventing damage by natural or augmented populations of cabbage maggot to roots. This may be because cabbage maggot eggs are laid on the soil surface near the root, so surface applications may place the nematodes closer to the hatching maggots than a subsurface application can.
Although treatments did not eradicate the maggot population, the amount of deep feeding scars caused by the cabbage maggot (that may later lead to loss of plants or a reduction in yield) was significantly reduced. Now inexpensive application methods need to be developed so commercial growers can utilize nematodes. Perhaps devices to inject nematodes onto or into the soil around the base of each plant can be combined with fertilizer and water application equipment already present on many mechanical bare root transplanters.
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