Floriculture Greenhouse Update

Inspecting Incoming Plants

Monday, 08 March 2010 13:11

Inspect incoming plants carefully for signs of insects, diseases, weeds and cultural problems. Inspect the entire plant - leaves, stems and roots for signs of pest activity and for general health. Look for any distorted new growth on incoming plugs and transplants that might be caused by thrips. Blackened, firm stems and leaf spots on garden impatiens and New Guinea impatiens are signs of Impatiens necrotic spot virus (INSV). INSV test kits are useful for quick tests of suspicious looking plants.

Look on the undersides of leaves for spider mites. They are often found along the mid-vein of ivy geraniums, ipomea, thunbergia and other susceptible plants. On ivy geraniums, spider mite damage is similar to damage caused by thrips and oedema.

Inspect root health also. Roots should be white with vigorous growth. Roots that are brown or decayed are evidence of root rot disease or may be caused by overwatering or high soluble salts.

When handling and cleaning incoming plants, work in blocks and wash hands thoroughly between blocks of plants. If disposable gloves are worn, change or clean them between blocks. This will prevent spreading infectious diseases that are transmitted mechanically, such Bacterial leaf spot on geraniums and Tobacco Mosaic Virus on petunias and related crops.
 
If at all possible, do not accept plant shipments with serious insects or diseases with wide host ranges, and are difficult to treat. Do not accept plant material infected with incurable diseases, such as root rots, viruses, bacterial leaf spot diseases, or foliar nematodes. If you need confirmation, isolate a few plants showing symptoms and send them to a diagnostic laboratory. If you find isolated evidence of some insect activity, for example, aphids, and decide to keep the shipment, identify an isolated, quarantine area in which to keep the plants. Treat immediately and hold the plants in this area until you are sure that they are healthy, salable and free of pest problems. Only enter this quarantine area at the end of the day to avoid moving pest problems throughout your operation.

Tina Smith, University of Massachusetts

Garden Retailers and Late Blight

Wednesday, 17 February 2010 12:48

Late Blight caused by Phytophthora infestans – a very destructive and very infectious disease killed tomato and potato plants in gardens and on commercial farms throughout the eastern U.S. during 2009. Late blight occurs at some locations in the Northeast each year, however in 2009 infected plants were distributed through large local retail stores throughout the region (Ohio to Maine) during June, and outbreaks were reported over this entire region by early July. This, combined with the cool, wet growing season and the exceptionally contagious nature of the disease during cool, rainy, windy weather all contributed to a disastrous year for farmers.

Garden retailers can help prevent the spread of late blight in gardens and on farms this growing season and provide customers with the facts about this disease.

Grow your own transplants from seed or purchase locally grown plants
Late blight is not seedborne in tomatoes (however, it is tuber-borne in potato), so tomato plants started from seed locally (in the Northeast) would be free of the disease. Growing your own transplants from seed or purchasing from a reputable local grower will ensure a healthy start to the season for your customers and local farms.

Provide disease-resistant or tolerant varieties
      Tomatoes: Disease-resistant or tolerant varieties of tomatoes exist, however seed is in limited supply this year. ‘Mountain Magic’, ‘Plum Regal’, and ‘Legend’ are three varieties with resistance or tolerance to late blight. Note that the variety ‘Legend’ is the only late-blight resistant variety for which seed is readily available this year. In addition to late blight, each year tomatoes become infected with early blight and Septoria leaf spot, which look very similar. If possible, also provide tomato plant varieties that are resistant or tolerant to early blight for your customers, such as the varieties ‘Mountain Fresh’, ‘Mountain Supreme’, and ‘Plum Dandy’ and others.
      Potatoes: Purchase certified, disease-free seed potato from a reputable source, and ask your supplier about their source of seed and if it was inspected in the field for late blight. Seed potato from the northeast are less likely to carry the disease.

Inspect transplants for signs of disease
If you purchase plants to sell, inspect all transplants for stem, petiole cankers or leaf blight as long as plants are on the shelf. Teach your staff what to look for, using the web-links below. If you suspect a late blight infection, use your Plant Diagnostic Lab to confirm if late blight is present.

Know the FACTS for Staff and Customers
Train employees and provide information to your home gardening customers.
* Potatoes that freeze or fully decompose will not carry the pathogen over winter.
* Tomatoes will not carry late blight over the winter, because freezing kills the whole plant.
*  Tomato seed, even from fruit that was infected with late blight, will not carry the pathogen, so no need to worry about the tomatoes left behind in the garden or compost pile. Certain perennial weeds can become infected with late blight, but none of their above-ground tissues live through the winter.
*  Late blight will not survive on tomato stakes and cages.
* The biggest threat for overwintered disease in New England is on potatoes. In the spring, advise home gardeners to inspect last year’s potato plot and any compost or cull piles for volunteer potato plants that might come up. If they find potato plants, pull them out and put them in the trash or destroy them. If tubers were infected and survive, then the late blight could grow upward from the tuber, infecting the stem and producing spores when weather conditions are favorable. These spores could then disperse to other tomato and potato plants.
* During the growing season, pay attention to pest alerts to learn about whether late blight has been observed in New England, and what actions you need to advise to customers. Pest alerts will be updated on the UMass Extension Vegetable Program Website, www.umassvegetable.org   

Photos: Symptoms on stems, leaves and fruit (Cornell)
Photos, FAQ, Fact Sheets (Cornell)

Tina Smith, University of Massachusetts

Hunter flies and Shoreflies on Sticky Cards

Tuesday, 16 February 2010 14:46

Hunter flies are becoming more common on sticky cards in greenhouses. The Hunter fly (Coenosia attenuata) is a greyish, predatory fly in the same family as the housefly and similar in appearance, but smaller than the common housefly. Some growers confuse them with shore flies. Adult shoreflies also resemble small houseflies, with their short robust bodies, short legs and short antennae, but are smaller than the hunter fly, darker in color and have characteristic five clear spots on the wings.

The adult hunter fly preys on other flying insects, catching them in flight. It feeds on fungus gnats and shoreflies, but also on other flying insects such as leafminer and, to a lesser extent, whiteflies. The larvae live in the soil and are generalist predators on soil-dwelling organisms such as fungus gnat and shorefly larvae.

Hunter flies are originally from Europe. They were first found in the United States in October of 1999 at a commercial greenhouse in upstate New York. Adult females lay eggs in the soil that hatch in about 5 days. The hunter fly larvae seek other soil dwelling insects such as fungus gnat larvae as prey. Larvae grow for about two weeks and then pupate in the soil for two weeks.

Photos: Hunter fly adult, Hunter flies on sticky cards, Fungus gnat and shorefly on sticky card, Shoreflies and others on sticky cards

More Photos: Fact sheet on fungus gnats and shoreflies including photos of hunter flies, shore flies, fungus gnats and common parasitic wasps found on sticky cards.   Need to scroll to figures 11-14

Leanne Pundt, University of Connecticut
Tina Smith, University of Massachusetts