Field and laboratory studies of the effect of urea on ascospore production of Venturia inaequalis (Cke.) Wint

Abstract

Applications of urea after harvest but before leaf-fall restricted perithecial production by Venturia inaequalis. Immersion of detached leaves in urea appeared to be the most effective method of preventing perithecial formation, although spraying attached leaves was equally effective when leaf abscission occurred within a week of treatment.A high nitrogen content within the leaf was one of the major factors contributing to suppression. Urea-treated leaves decomposed rapidly, thus destroying the overwintering substrate for the fungus.urea, followed by a second (pre-bud-burst) application at 2 yo, ascospore production in the spring was suppressed. The second treatment appeared to prevent the release of ascospores from mature perithecia.When apple plants (clone M. I I I ) were sprayed in autumn with 5

Effects of Shredding or Treating Apple Leaf Litter with Urea on Ascospore Dose ofVenturia inaequalisand Disease Buildup

“…In the small-plot study, urea was most effective when applied to the trees in autumn before leaf fall, and the percent reduction in number of ascospores trapped was comparable to the percent reduction in the number of pseudothecia or ascospores reported in several other studies (6,8,9,11,17,44,46,55,58). The treatment was not repeated because of grower concern that urea applied to the trees in late autumn may result in nitrogen accumulation in buds at a level that may stimulate new growth resulting in winter injury under some conditions.…”

“…A post-leaf fall treatment of urea was usually more effective when applied in spring, and the percent reduction in ascospores trapped was similar to the reduction in pseudothecia or ascospores reported for a spring urea treatment in other studies (6,18,44). The two least effective spring urea treatments were in 1993 and 1994.…”

“…The authors are aware of only two studies that considered the potential of a urea treatment to reduce primary scab lesions. In England, one-half of two large, severely scabbed Bramley orchards received a postharvest, pre-leaf fall application of 5% urea, and lesions on blossom-spur leaves on the treated trees were reduced by 59 and 46%, respectively, the following spring (6). In France, severely scabbed (>30% foliar scab) Golden Delicious and Starking Delicious trees sprayed with 5% urea after harvest but before leaf fall had 1% foliar scab at the end of the primary season the following spring (5).…”

A method to monitor airborne Venturia inaequalis ascospores using volumetric spore traps and quantitative PCR

“…through leaf removal or shredding) is thought to reduce the incidence of primary infections when fruit is most susceptible, and prevent epidemic build-up of apple scab through secondary infections (MacHardy 1996). Previous studies commonly used the evaluation of reduction in incidence and severity of scab lesions in combination with the labour intensive method of quantification of mature ascospores from leaf litter, using a squash mount technique, to analyse effects of chemical suppression of ascospore production (Burchill andHutton 1965, Burchill 1968;Gadoury and MacHardy 1986;Schwabe 1977;1980b). Weather models combined with methods to monitor ascospore maturation and predict potential ascospore dose have been shown to be effective in predicting apple scab infection risk (MacHardy 1996;Gadoury et al 2004).…”

EFFECT OF AMMONIUM NITROGEN AND AMINO ACIDS ON PERITHECIAL FORMATION OF VENTURIA INAEQUALIS

“…Urea apptied to apple foliage in the autumn prevented perithecial production (3,4). The mode of action of urea in suppressing perithecial formation is not known, but the high nitrogen content of the leaves appears to be involved (2,8,15). This paper reports further investigations on the effect of nutrients on the formation of perithecia of V. inaequalis.…”