THE EFFECT OF TEMPERATURE UPON THE PRE-ADULT LARVAE OF THE BULB NEMATODE ANGUILLULINA DIPSACI (KÜHN, 1858) GERV. AND v. BEN., 1859, IN RELATION TO TIME AND MOISTURE

Abstract

In a moist environment, a minimum exposure of 120 min. at 110–113°F. is required to destroy pre-adult larvae of the bulb nematode Anguillulina dipsaci (Kühn, 1858) Gerv. and v. Ben., 1859, but progressively shorter exposures are required as the temperature is raised. At 116.5–118.5°F. the lethal exposure is 60 min. and at 118.5–120°F. an exposure of 30 min. is required.In a dry environment exposures of 150 min. to temperatures as high as 140°F. are not lethal to pre-adults and the heat treatment does not affect their ability to induce the characteristic symptoms of infestation in barley seedlings.The pre-adults are more resistant to heat than any other stage in the life history of the nematode.The data suggest that the ineffectiveness of the standard hot water treatment when applied late in the season is due to the fact that the major development of pre-adults takes place after the bulbs are lifted, and also because the masses of dormant pre-adults are often well isolated from the moisture of the bath by the bulb scales and corky basal plates, and are more resistant to heat in a dry, compared with a moist, state. It is recommended that the hot water treatment be employed not later than four weeks after lifting when the lifting is done as soon as the foliage dies down.A pre-soak is suggested as a possible means of increasing the effectiveness of the standard hot water treatment.