PREVALENCE, SEVERITY, AND ASSOCIATION OF FUNGAL CROWN AND ROOT ROTS WITH INJURY BY THE CLOVER ROOT CURCULIO IN NEW-YORK ALFALFA

A survey of 61 randomly selected alfalfa fields in four physiographic regions of New York was utilized to assess the incidence, severity, an d fungal flora associated with crown and root rots, as well as the inc idence and severity of injury by the clover root curculio (Sitona hisp idulus) and its possible association with root diseases. Five stratifi ed random subsamples, each comprising four to nine alfalfa plants, wer e evaluated from each field. Crown and root rot occurred in every fiel d surveyed, with average tissue necrosis estimated at 21, 27, and 37% in plants from 1-, 2-, and 3-yr-old stands, respectively. Fusarium oxy sporum, F. solani, Phoma sp., and F. avenaceum were the pathogenic fun gi predominantly associated with necrotic roots, accounting for 25, 21 , 12, and 4% of isolations, respectively. Inoculation of alfalfa plant s with each of 28 randomly selected isolates of F. oxysporum and 18 of F. solani resulted in root and crown necrosis similar to that observe d in the field, but no isolate induced rapid wilting and shoot death a s did reference isolates of F. oxysporum f. sp. medicaginis, causal fu ngus of Fusarium wilt. Every field and 92% of all individual plants ex hibited injury from clover root curculio. The number of wounds that br eached the root cortex ranged from 0 to 45 per plant and averaged 2.6, 5.5, and 6.1 for 1, 2-, and 3-yr-old plants, respectively. Epidermal scarring and deep feeding wounds were highly correlated as measures of clover root curculio activity. There were highly significant, positiv e linear correlations between average number of deep wounds and averag e tissue necrosis of plants for fields of each age, suggesting that cl over root curculio injury had predisposed alfalfa plants to more sever e crown and root rot. Although injury levels were generally lower in t he two northern counties sampled, plants from individual fields in eac h physiographic region showed pest injury levels that potentially coul d result in economically significant reductions in yield. Reduction of pest-induced losses in New York alfalfa will rely on concomitant cont rol of clover root curculio and fungi that cause crown and root rot.