Tuesday, November 12, 2013

Recurring Pythium in the Greenhouse - Poinsettia Root Rot

One of our local greenhouse growers struggled with Pythium infections in pansy earlier this year.  Now, poinsettia are infected with the same root rotting/damping off fungus. 

So, why would Pythium be a recurring problem?  Simple.  Sanitation.

Sanitation is critical for greenhouse production, landscapes, orchards, and gardens.  In this greenhouse, fungal propagules are obviously spreading via debris, hoses, shoes, tools, drainage water, and more.  Also, Pythium favors soilless mixes, where there's no competition.  Growers should verify that potting mix is not contaminated and that containers are sterilized before reuse.

Moreover, greenhouses must be disinfested between crops, so that disease-causing propagules are not carried over from one crop to another.  

Once a greenhouse is infested with Pythium, fungicides are required for disease management.  A single fungicide application will not be sufficient to manage disease, so a regular schedule should be employed.  Rotate fungicides by FRAC group (mode of action), avoiding two consecutive applications of any particular group and observing maximum numbers of applications per season.  Fungicides effective against Pythium include: 
·         mefenoxam (Subdue MAXX) FRAC 4
·         etridiazole (Truban/Terrazole) FRAC 14
·         propamocarb (Banol) FRAC 28
·         dimethomorph (Stature) FRAC 40
·         phosphorus acids (Aliette, Alude, Vital) FRAC 33
·         etridiazole + thiophanate methyl (Banrot) FRAC 14 + 1


For more information on disease management of poinsettia or other greenhouse crops:

Fungicides for Management of Diseases in Commercial Greenhouse Ornamentals http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-3.pdf
Poinsettia Diseases  http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-H-2.pdf


Thursday, November 7, 2013

Stunted Pines and Brown Needles: Diplodia Tip Blight

Diplodia tip blight is a serious disease of mature Austrian, Scots (Scotch), and Mugo pines in Kentucky. The disease is caused by the fungus Sphaeropsis sapinea.  In the landscape, tip blight is normally not observed until pines reach about 12 years old and begin to bear cones. Continuous infections (3 to 5 consecutive years) can greatly weaken and eventually kill affected pines.

Infection occurs in spring; however, disease symptoms become more obvious in mid- to late-summer and fall. Needles in early stages of development stop growing as a result of shoot infections. These stunted needles eventually die and turn straw-colored (Figure 1). Infection progresses to healthy needles and cones.

Disease Management:

·         Apply fungicides (chlorothalonil, propiconazole, or thiophanate methyl) to trees just as buds swell in spring. Apply a second spray when the candles are about half elongated and a third spray as needles begin to emerge from the needle sheaths.
·         Remove and destroy dead twigs, branches, and cones as they occur. Do not prune when trees are wet.
·         Destroy all blighted needles, twigs, and cones debris as they fall to the ground.  The fungus overwinters in debris, especially infected cones and diseased needles.
·         Trees under stress tend to be more susceptible to tip blight. Fertilize and water trees as needed to promote vigor.

 For more information on tip blight or pine diseases:

Needle Cast Diseases of Conifers  http://www2.ca.uky.edu/agc/pubs/id/id85/id85.pdf

Twig, Branch, and Stem Diseases of Pine  http://www2.ca.uky.edu/agc/pubs/ppa/ppa16/ppa16.pdf

Department of Plant Pathology, Extension Publication page  http://www2.ca.uky.edu/agcollege/plantpathology/extension/pubs.html