Monday, March 31, 2008

Greenhouse - More on New Guinea Impatiens: Pest Issues

The following is additional information on New Guinea Impatiens insect and disease control from the University of Maryland.

Diseases to watch for:

- Pythium- root and stem rot. Symptoms include stunting, yellowing, wilting, and soft brown roots. Development promoted by over-irrigation and over-fertilization.
- Botrytis- look for the fuzzy gray spores on senescing flowers and dead plant material. Requires film of water on plant surfaces for several hours to germinate.
- Rhizoctonia- can cause root rot and stem cankers. It is called “web blight” when the mycelium grows on aboveground plant parts causing them to “melt down”

Foliar Leaf Spots

- Alternaria- fungal disease which requires a film of water and moist conditions for infection and sporulation.
- Myrothecium- attacks injured or stressed plant tissues and causes necrotic lesions with dark rings, often on the leaf margin. Green/black spores on white sporodochia are characteristic of this disease.

Virus – Tospovirus

- INSV (impatiens necrotic spot virus) some leaves show dark spots and rings, while others can have mosaic symptoms. If virus transmission is going on in the greenhouse, the tolerance level for thrips drops to almost zero. Monitor for thrips using sticky cards.

Thrips control: rotate between materials. Pedestal controls larvae of thrips. Pylon at the high rate of 10-15 oz/100 gallons works. Conserve can be one of the choices, but don’t just rely on this chemical for solving all of your thrips problems. Fortunately the suppliers are doing a better job of cleaning up tospovirus and we are seeing less and less of it. Still stay alert and look for the symptoms on plants. If you see it show up in your greenhouse immediately rogue out the infested plants.


Examine the undersides of foliage for mites. We usually see mites injuring New Guineas grown in the hottest parts of the greenhouse, especially hanging baskets and plants on south walls. Control: Akari, Avid, Floramite, Pylon, Judo, horticultural oil.

Information from the March 28, 2008 edition of the Greenhouse TPM/IPM Weekly Report
from the University of Maryland Cooperative Extension

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