Insect and disease update in the greenhouse

Spring’s change in the weather can make it tricky to forecast greenhouse crop needs. Daily and hourly assessments are critical.

Adjusting your growing strategies based on the weather can be challenging to say the least. Over the past four weeks, Mother Nature has brought us sun but cool temperature, sun and 80°F temperatures, snow and cold, and currently below average temperatures and clouds. Walking your crop daily or multiple times a day is important this time of year to assess your crops’ needs. Even though this is common knowledge, it’s overlooked and that’s when problems happen. If they’re caught early, some issues can be managed while others may cause a loss of some of the crop; but minimize the issue and isolate the problem.  

Insect issues

Thrips: Growers who did not have their thrips populations under control prior to plants blooming are struggling. You need to be diligent in your insecticide applications from the recommended list on a 5 to 6 day application schedule in order to knock down the immatures and adults. 

Aphids: Reported being seen everywhere – not seeing them yet? Look at the weeds along walks, walls and under benches. I’m pretty sure you can find them. See the 2011 Insect Control Research Results.

Mites: Not super heavy, but if your scouting has been lax, they may be showing up on some of their favorite crops like Cordyline and Bon Bon Begonia’s.

Whiteflies: Being reported on Bacoppa. If you have lantana, I would make sure to put a card in that area.

Disease issues

If you have been struggling with thrips and your plants are looking suspicious, have them checked for INV or TMV, or both. You can purchase amino strips and test in house or submit samples to the MSU lab.

Water management is imperative under these weather conditions. These pathogens have been reported around the state: root rots, Botrytis and Alternaria spp. Symptoms of Alternaria vary depending on the host, but may include dark-colored leaf spots, lesions with concentric rings within the lesion, and cankers. Spots may coalesce resulting in blighting of foliage. Petals of some plants may be infected. Spores are produced on the plant surface and are spread by splashing water, air movement or by moving infected plant material. Maintain adequate plant spacing to allow for good aeration to reduce humidity levels around plants. Alternaria spp. requires leaf wetness for germination and infection; reduce durations of leaf wetness periods with good timing of overhead irrigation. Regular fungicide applications will likely be necessary to reduce losses on especially susceptible hosts. In fungicide control trials products containing chlorothalonil, mancozeb, iprodione, or fludioxonil have provided excellent disease control.

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