Diseases

Phytophthora Crown Rot and Stem Canker

Calibrachoa cv .Million Bells Crackling Fire was diagnosed with Phytophthora crown rot and stem canker. Symptoms include wilting, decline, and plant death although a fairly healthy root system is present. Phytophthora like Pythium is a lower fungus favored by excess moisture and excess nitrogen fertility. Unlike Pythium, species of Phytophthora are more aggressive, more likely to be host specific, and less frequently found in greenhouses. The most likely source of origin is plant material.

Tospovirus

Tospovirus is a virus family that includes impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV). These viruses are spread by Western flower thrips. The virus is brought into the greenhouse on vegetatively propagated plants or seedlings that have been exposed to the virus. Once the thrips in the greenhouse pick up the virus they can transmit it to weeds and crops. Plants can be tested for INSV and TSWV by your University diagnostic lab or by easy to use ImmunoStrips (dip-stick tests) that are available from Agdia. There is no cure for these viruses.

Downy Mildew on Snapdragon

Downy mildew (Peronospora antirrhini) was reported on snapdragons (Antirrhinum majus) this week. Downy mildews have become an increasing problem in the horticultural industry and are currently causing serious losses in many floricultural crops including rose, pansy, viola, coleus, alyssum, salvia, and snapdragon. The pathogens are very different from Powdery mildews-they attack different plants under very different environmental conditions, and are controlled by different classes of fungicides. Most of the Downy mildew fungi are host specific and infect only one plant family.

Septoria Leaf Spot

The rainy weather in May and early June has encouraged the development of fungal leaf spots on various herbaceous perennials. Rudbeckia can become infected by leaf spots caused by a variety of fungi including: Alternaria, Cercospora, Colletotrichum, Phyllosticta or Septoria. Rudbeckia can also become infected with an angular leaf spot caused by a bacterium. Discoloration on the leaves may also be due to nutritional imbalances. Submit samples to your diagnostic laboratory for confirmation.

Botrytis Ghost Spot on Tomatoes

Growers are all too familiar with Botrytis Blight, one of the most common diseases in the greenhouse. It is easily recognized by the fuzzy gray spores that develop during humid conditions. On greenhouse tomatoes, Botrytis develops near pruning wounds, and on older, weakened foliage. From the petiole stumps, it can progress to the stems, girdling and killing plants. Sometimes, Botrytis invades the calyx end of the fruit, so that a soft watery rot develops.

Black leg on Geraniums

Black leg is one of the most common diseases seen on geranium cuttings during propagation and on young plants. The first symptom is brown, water-soaked tissue at the base of the cutting. This turns shiny black and can quickly spread 3 or 4 inches up the cutting stem. Eventually the tops of affected cuttings and plants wilt, yellow and die. Fungus gnat larvae are often found in infected cuttings.

Soil Testing and Disease Diagnostic Laboratories

Prevention and correct identification of insect, diseases and nutritional problems can help you save money by reducing crop losses, improve the quality and marketability of your crops and prevent the application of the "incorrect" pesticide or fertilizer. Here is a listing of the laboratories in Massachusetts, Connecticut and Rhode Island.

Massachusetts University of Massachusetts, Amherst Soil and Plant Tissue Testing Laboratory http://soiltest.umass.edu

Tobacco Mosaic Virus (TMV)

Tobacco mosaic virus has a wide host range but is of special concern on solanaceous crops. TMV has been reported on ajuga, begonia, calibrachoa, chrysanthemum, cyclamen, epimedium, gazania, geranium, gerbera, helianthus, impatiens, lisanthus, lobelia, lysimachia, New Guinea impatiens, osteospermum, nicotiana, pepper, petunia, penstemon, tomato, torenia and verbena.

Thrips and Tospoviruses

Thrips populations are increasing with the warmer temperatures. I've observed thrips feeding upon numerous greenhouse crops including ivy geraniums, double impatiens, tomato bedding plants, plus greenhouse weeds including chickweed, galinsoga, etc.

Tospoviruses have also been detected on greenhouse crops including impatiens, double impatiens etc.

Heuchera Rust

Rust fungi are obligate parasites that need to grow and develop on living plants. Fortunately, they don't readily kill infected plants, but their damage can be unsightly. Rust fungi tend to be host specific, affecting closely related plants. They often have complex life cycles. Some types of rust need two different hosts to complete their life cycle, such as Fushsia rust. Other types of rust only need one host to complete their life cycle, such as geranium rust or rust on hollyhock.

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