Usually by late August we see a significant drop in the number and intensity of pests in the landscape and nursery. Well, except for Japanese beetle….
This was a banner year for diseases and a lot of the Gymnosporangium rusts did very well too. The above photo is a newly-formed gall of cedar-apple rust on Juniper. These galls are perennial and grower bigger and bigger each year (they turn reddish brown after the first sporulation event). The bigger the gall, the greater the spore release to the rosaceous hosts. So, training your eye to detect these galls and pruning them out and significantly reduce disease on the alternate host next year.
As crazy as it sounds, fireblight is still active and new infections are showing up on pear and apple each weed in some areas. Place a bag over the affected twig and prune out the twig well below the symptomatic tissue. Do this sanitation practice only in cool, dry weather. Be careful not to knock infected twigs around too much, you might end up increasing the amount of disease.
Nectria canker is starting to show up on winter killed tissues on trees and shrubs. Nectria is a weak fungal pathogen that infects tissues after they have been damaged. Although sometimes they are a primary pathogen, usually they are not the cause of the tissue dieback.
Spruce spider mite and two spotted spider mites are very active this month. Their feeding injury causes small spots of chlorosis causing a “bronze” appearance to the foliage. In the above photos you can find injury from spruce spider mite on Eastern white cedar (Thuja occidentalis) and injury from two spotted spider mite on Hydrangea paniculata.
We are also seeing injury from Apple leaf-curling midge on some ornamental Malus (crabapple and fruiting apple). The larvae are maggots (midge larvae) and feed from inside the protection of curled leaf edges. The damage is not usually significant as it happens late in the season.
Take care out there!