Temecula Valley Rose Society
Rose Care Corner, August 2007By Frank Brines – Consulting Rosarian
I n the summer heat, reduce fertilizing roses. Moisten soil to 1 foot when watering. Water only in the morning so the leaves will dry by evening and not increase the chance of having powdery mildew disease. Hosing off the dust will help prevent the disease. Also a spray containing neem oil will assist in prevention. Another way to inhibit powdery mildew from getting started is to spray once a week with a solution of 1 tsp baking soda, 1/4 tsp mild soap (not detergent) and little cooking oil. Hose off between sprayings.
With the heat, pests also become a bigger problem. Like powdery mildew, spider mites thrive on dusty plants and they are especially fond of roses. Help prevent them by removing all foliage within eight inches of the soil level. As for powdery mildew, regularly rinse off the dusty foliage (especially the undersides) with a strong water spray. The mites that are washed off have low ability to reinfest. Whiteflies can also be tackled with strong blasts of water each day, or with a soapy water spray, which is less toxic to other insects.
On that note, if you have used pesticides in the past but are thinking of being more organic and enlisting the aid of beneficial insects (e.g., ladybeetles, praying mantis, lacewings, etc.) don't be discouraged if their populations are slow to build up, even if you introduce them deliberately. Pesticide residue may persist for a year or more, contaminating (but not killing) the pests that the beneficial insects eat. Since the beneficials are higher on the food chain, they may accumulate pesticides and be adversely affected. Over time, if you refrain from spraying insecticides, the beneficial insects will arrive on their own to consume the pests. Also, be aware that there must be pests for the beneficials to consume when you release them, or they will go elsewhere, which is sometimes disappointing to gardeners.
Continue to prune away suckers, unwanted branches, and spent blooms; gently shape your roses after pruning.
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