NDSU Extension - Williams County


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Post Flowering Nitrogen-Will It Pay? - Plum Pockets, Black Knot, and More

Published July 17, 2013
Post Flowering Nitrogen-Will It Pay? - Plum Pockets, Black Knot, and More

Plum pockets

Post Flowering Nitrogen – Will It Pay

Current crop conditions certainly give optimism for some favorable grain yields. However, above normal grain yields often result in lower protein of our cereal crops. Research has shown that applying nitrogen to spring wheat immediately after flowering can increase protein at least 0.5% to about 1%. But, Dave Franzen, NDSU Extension Soils Specialist feels the economic incentive to apply 30 pounds N/acre to archive this increased protein content is low.  Franzen calculates the cost of applying UAN (mixture of urea and ammonium nitrate) with 10 gallons of water is about $20 per acre, possibly more. A 50 bushel yield and 15 cent premium per bushel for a one percent increase in protein content only produces $7.50 per acre in added revenue. He acknowledges the presence of an overwhelming quantity of lower protein wheat might result in higher protein premiums and higher low-protein dockage at harvest time. Even the new generations of farmers have experienced this. A 40 cent premium for an added one percent protein would pay for the additional nitrogen applied when the wheat berries are in the watery ripe stage.

Plum Pockets, Black Knot, and More

This past week I received a couple samples of plum stems, both with deformed, hollow fruit. In both cases the fruit was unusually large. I identified the problem as a fungus disease commonly called plum pocket (Taphrina Communis). This disease most often appears on native species, especially Canada plum and wild, or American plum. It is less common on domestic (European) plum and uncommon on Japanese plum.  Except for removing the infected fruits, there is very little one can do this year. However, next spring before the buds break open, spray the tree with lime sulfur.  I continue to receive calls and samples of cherry and plum branches which have abnormal black growth. This is called black knot (Apiosporina Morbosum), another fungal organism. Because there are many chokecherries and wild plums throughout the area the fungal spores of black knot are abundant. It has been my observations that the disease is more prevalent during abnormally wet periods, certainly the case this year.  Management of black knot involves pruning out the infected branches making sure to cut at least four inches into the healthy wood. Before making another cut, be sure to dip the cutting instrument into a disinfectant such as household bleach. The bleach can be corrosive to metal so it is suggested to apply oil before storing the equipment.  If black knot becomes a yearly problem, consider applying lime sulfur as a dormant spray in the spring after removal of knots. Another preventive option is to apply thiophanate-methyl when the tree is 1) dormant, 2) pink bud, 3) full bloom, and 4) three weeks after full bloom.  It appears to me some cherry and plum trees have resistance to black knot. If you are lucky enough to have such a tree in the yard, then a decision to remove a diseased one will be easier.  Another problem brought to my attention this past week was cedar-apple rust of Juneberry. This disease, again fungal, requires two different hosts to complete their life cycles. They overwinter as galls or witches’- brooms on junipers. In wet weather, orange gelatinous spore-leaving structures develop. These structures can develop several times between May and August, producing spores each time that can infect Rosaceous hosts such as apple, crabapple, hawthorn, and juneberry. On these hosts, infection results in small yellow-orange lesions on the upper surface of leaves and young fruit. Damage to Rosaceous hosts may develop as reduced fruit quality and minor to almost total defoliation of susceptible cultivars.  It is my opinion that managing or preventing damage to the Rosaceous plants is difficult if not impossible. Removing the juniper host plant is difficult because all within a 2 to 4 mile radius must go. If removing an alternate host (within the juniper or Rosaceous plant) is not possible, picking the galls on pruning the witches’ brooms off the juniper may keep the disease to a manageable level. There are several fungicides that can be used to protect ornamental Rosaceous hosts.

-Warren Froelich

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