August 2010 - Summertime Pests & Diseases

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Repotting should be done by now, but keep an eye on those oddball species that like to grow roots as they flower. Many bifoliate cattleyas need to be repotted just as they come into flower. Some like C bicolor with 3 foot pseudobulbs are particularly frustrating since buds emerge about the same time as new roots. It is not unusual to see this same characteristic in their offspring.

Insects are cold-blooded, which means they grow faster when greenhouse temperatures are warm. This is true for both scale insects and mobile pests such as roaches. Roaches, mealybugs, and other mobile animals that live in pots can reduce all your carefully protected root tips to little white nubs. Unfortunately, this mostly happens at night so there is always some uncertainty as to the identity of the offending culprit. If you are a night owl, a quiet visit with your flashlight to your growing area at night may get you a quick view of the culprit. If you are having this problem, mix up a 5 gallon bucket of liquid Sevin, 1 teaspoon per gallon and dip the entire orchid pot for a minute or two and see what comes out. Roaches will make themselves known, but many smaller animals such as snails & slugs will just die in the pot. Either way, problem solved. For hobbyists who place their orchids outdoors in summer and bring them inside in winter, remember this treatment to avoid importing pests.

There are a few orchids in my collection that should love the heat of summer, but Angraecum hybrids and species often develop rots in their new leaves as they emerge. Keep a bottle of household hydrogen peroxide in the growing area. After you water, put a few drops in the crown of angraecums or any other monopodal orchid (phals, vandas, etc) that grow on a vertical stem and the rot problem will disappear.

Summer is a time of both heat and humidity. If you are growing outdoors don’t forget last month’s watering advice. Always keep in mind that cool weather will require a reduction in watering frequency. There is always the possibility here in the Southeast of a tropical system lasting for days. Tropical systems import fungal and bacterial spores. The heat and humidity that accompany these storms encourage their growth. These disease-causing organisms are always around and there is nothing that can be done.

If you grow outside and your orchids are naturally watered by the rain, it may be necessary to provide some shelter if several days of tropical rain is expected. In my greenhouse, I also spray down all surfaces under benches, on walls, etc with a strong anti-biotic. Copper Sulfate (Kocide) works well as can a solution of Clorox. However, these products can damage orchids if they get on leaves. If orchids are wet there is less danger or a less toxic product can also be used.
Kocide, used in a more dilute form is safe to use on some orchids, but only if the water you mix it with is on the basic side of the pH scale, i.e. above 7. Even then, there can be damage on tender new phal leaves as well as to other sensitive orchids. There are other products such as Phyton 27, approved for direct application to orchids. It is easier to prevent infections than cure them.
Once the tropical system has passed it is wise to treat your orchids with some type of anti-fungal or anti-bacterial agent. Some hobbyists that have small collections use the same hydrogen peroxide noted above, place it in a spray bottle and spray their plants. Remember to keep air moving around your orchids. Once the rain stops and humidity drops it is also a good idea to let your orchids dry thoroughly.