• Root and Crown Rot of Apple Trees Caused by Phytophthora

      Matheron, Michael; Young, Deborah; Matejka, Joe; Kilby, Michael W.; Bantlin, Marguerite (College of Agriculture, University of Arizona (Tucson, AZ), 1990-12)
    • Seasonal Variation in Susceptibility of Citrus Rootstocks to Phytophthora

      Matheron, Mike; Matejka, Joe (College of Agriculture, University of Arizona (Tucson, AZ), 1986-12)
      Phytophthora parasitica and P. citrophthora are routinely recovered from diseased citrus groves in Arizona. Stem sections were collected monthly from Citrus macrophylla, rough lemon, .sour orange, Cleopatra mandarin, Troyer citrange and Citrus volkameriana. Stem pieces were wounded, inoculated with mycelium of P. parasitica or P. citrophthora, then incubated for 7 days at 21° C in moist chambers. For all tested rootstocks, the smallest cankers were produced on tissue collected in December, January and February, the winter dormancy period for citrus in Arizona. The period of higher susceptibility ranged between March through November, depending on the rootstock tested. Apparently, these six citrus rootstocks possess seasonal differences in their susceptibility to P. parasitica and P. citrophthora.
    • Trunk Application of Phosphorous Acid and Two Other Fungicides for Control of Phytophtora Gummosis of Citrus

      Matheron, Mike; Matejka, Joe (College of Agriculture, University of Arizona (Tucson, AZ), 1986-12)
      Gummosis caused by Phytophthora parasitica and P. citrophthora is a serious problem in Arizona citrus groves. In a 15-year-old Orlando tangelo planting at the Yuma Mesa Agricultural Center, a 20 cm section of trunk on each tree was painted with phosphorous acid, metalaxyl or fosetyl-Al. After treatment, pieces of bark were periodically removed from within, as well as below, the treated area and inoculated with P. parasitica and P. citrophthora. After 117 days, both Phytophthora species were inhibited on bark treated with phosphorous acid, metalaxyl or fosetyl-Al. Canker development was also reduced on bark tissue sampled 10 cm below the site of treatment. The results suggest that trunk application of phosphorous acid, metalaxyl or fosetyl-Al can provide effective protection against Phytophthora gummosis of citrus.