How Not To Screw Up Your Poinsettia Crop By Dean M. Krauskopf Michigan State University Extension How Not To Screw Up Your Poinsettia Crop: So far the crops that I have seen look good. Rooting was on schedule as long as media temperatures were maintained above 72 degrees, there wasnít much internode elongation and few insect and disease problems. However, the next four to five weeks are critical to a good crop so donít relax. Here are a few things that need your attention: Donít over fertilize. Dr. John Biernbaum has repeatedly shown that poinsettias grow very well at 150-200 ppm NO3-N as long as there is less than 10% leaching. Itís my observation that plants grown at lower fertility have larger, more developed root systems. While I canít prove it, I think plants grown at these lower rates also have a lower incidence of root rot. Donít allow internodes to stretch. While you can prevent internode elongation, you canít make them shrink so prevent the problem by keeping a close eye on DIF. The weather here in Michigan has been stranger than usual - sunny days with low humidity and cool nights - a large positive DIF unless youíre heating at night. Run the numbers - which costs you less -fuel to heat at night or applying growth regulators? Spacing plants on time will also prevent internode stretch. Donít pinch or apply drenches until the root system is developed. When you pinch a plant, most of the photosynthate goes to the developing tops and the roots can ìstarve.î If you pinch before roots are visible at the edge of the media, the root system will tend to be smaller than if you had waited a few more days. The same goes for growth regulator drenches. A too small root system cannot support the quality plant that is necessary for todayís market. Donít apply any insecticides, fungicides or growth regulators when the plants are stressed by high temperatures. Materials that you have used many times with no problems can cause severe phytotoxicity when the plants are heat stressed during application. If you have to spray or drench, do it very early in the morning when temperatures are as low as possible and make sure the media is moist before application. Donít apply an insecticide unless you have a problem (except for Marathon for whitefly control). Use potato disks to monitor for fungus gnat larvae (work from Dr. Ray Cloydís lab at the University of Illinois shows that 48 hours is the optimal time for leaving the disks on the media surface). Use yellow sticky traps to scout for thrips and whiteflies but remember that you should also closely examine selected plants for eggs and beginning infestations where the numbers of adults are small and may not be picked up by the yellow cards. Scouting individual plants is time consuming but will also pick up mite problems early before major damage occurs.