Managment
Vector Control
Sanitation
Alternate Hosts
Scouting
Preventing losses from tospovirus relies heavily on vector management. Thrips that have fed on plants infected with INSV will spread the virus to new crops. Monitor each crop with sticky cards to assess thrips populations on at least a weekly basis. Sticky cards should be placed throughout the crop with 6 per 2000 sq. ft. of bench space. Count thrips and record populations weekly to see if their numbers are rising. If thrips are present and increasing, use registered insecticides to control populations. Rotate chemicals from different classes and apply them early in the day when thrips are most active. Consider installing mesh screen to exclude thrips from the greenhouse vents and access doors.
For more information on thrips management, visit IPMNet.
Practicing good sanitation will greatly reduce many disease problems in the greenhouse. For tospoviruses, eliminate weeds and old plants that will not be used and keep the areas around the houses clean. Tospoviruses may be in weeds under the benches and outside of the greenhouse and remain present even when crops are gone. Eliminate all weeds. If the houses are to be shut down between crops, remove all weeds too. Flats of annuals that won't be sold or used, extra plants laying around, and stock plants held from year to year are potential problems if infected with tospovirus.
Exclude thrips with fine mesh screening (400 mesh) on air coolers and vents. Some growers have installed frame structures to support screening because the screen cuts down on air movement and additional surface area may be required. Don't bring plants into the greenhouse unless they are first examined for thrips. If there's an outbreak in one house, go into that house last during monitoring and watering rounds.
Purchase transplants and cuttings from reputable companies with good pest management programs and look carefully at incoming shipments. If possible, hold incoming plant material in a separate area until it can be checked for thrips and/or virus symptoms. Unpack boxes before they enter the growing area. If cuttings will be collected from your own stock plants, routinely check them for tospovirus because cuttings taken from infected mother plants will also be infected, even if few or very inconspicuous symptoms are present on the mother plant.
Tospoviruses are unusual in their wide host range and this is key to both diagnosing an outbreak as well as controlling it. Not only does INSV infect most of the major floral crops, it can infect many weeds, vines (for example Stephanotis) and ferns and foliage plants. What symptoms will you see? Maybe none. If symptoms are present, they may vary so widely that it appears to be a collection of different diseases. For example, cyclamen leaves will have ringspots, snapdragons may have stem lesions with dark ooze and coleus may be stunted. After a diagnosis of INSV in a greenhouse, examine every new symptom with virus in mind and follow up with testing.
Managing tospovirus fits perfectly into an integrated pest management (IPM) program. Regular monitoring for thrips and frequent examination of crops for symptoms are the priority in scouting for INSV. ELISA tests, whether done at a laboratory or on-site with kits that have been purchased, help confirm or eliminate INSV as the problem. Other problems may mimic INSV, for example phytotoxicity or some fungal and bacterial diseases, so having an ELISA or other laboratory test to confirm virus is prudent. The following are components of a scouting program for tospovirus.
Sticky cards - Various colors of sticky cards have been recommended for thrips monitoring in greenhouses. Yellow, blue and even hot pink have been used. Most importantly, replace the cards frequently and keep good records of thrips counts. Place extra sticky cards near vents and doorways to trap thrips entering the greenhouse.
Indicator plants - A "do-it-yourself" option for monitoring for INSV in greenhouses is to use indicator plants as an early warning system for virus. Ideally indicator plants, often petunia or fava beans, are placed in a house before a new crop enters. Non-sticky blue cards are put near the indicator plants to draw in thrips. If petunias are used, remove the flowers so that thrips will feed on leaves. Check the plants for papery spots. Symptoms should be distinct, within 3-5 days, if viruliferous thrips have fed on the leaves. An ideal indicator plant in this case is a plant that will show a non-systemic reaction quickly, and not become a reservoir for virus. However, indicator plants should be replaced after they show symptoms. Plants successfully used as indicators are the fava bean 'Aquadulce' from Stokes seed and several petunias including 'Calypso' from Ball Seed, and 'Super Blue Magic' from Park Seed.
ELISA and other laboratory confirmation - ELISA tests are used to confirm the presence of tospovirus. Because virus particles are too small to see without an electron microscope, visual inspection of leaves for virus particles is not practical in most scouting programs. ELISA kits, now commercially available, allow diagnosis of virus using antibodies that will react only with INSV or TSWV. Most University plant clinics and State Departments of Agriculture are also prepared to do ELISA for tospoviruses. There are other methods that some laboratories utilize, such as staining leaves for specific structures that form in infected leaves. A bioassy with an indicator plant series is also useful. Differing from the indicator plants discussed above, these plants are seedlings that are rubbed with sap from leaves to be tested and then observed for characteristic symptoms. For any laboratory test, taking a proper sample is the key to a successful diagnosis. Pick the portion of the plant with symptoms, or send a flat of small plants, or entire pots of larger plants.