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Ornamental Crops IPM E-newsletter, 2010

For Winter 2010

In this Issue:

  1. Fir Broom Rust: A new disease to watch for on firs
  2. Greenhouse Disease Preview, 2010
  3. Biocontrol for Western Flower Thrips
  4. Pest Management through Greenhouse Sanitation: Starting with the basics
  5. Late Blight of Tomato

Cornell IPM Team for Production Ornamentals
Disclaimer

Fir Broom Rust: A new disease to watch for on firs

Brian Eshenaur, NYSIPM,  bce1@cornell.edu

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Over the past few years fir broom rust has become a problem for some Christmas tree growers in Upstate New York.  As interest in and the acreages of Fraser and other firs increase we are likely to see more of this disease.  In the worst cases in NY, fir broom rust caused distortions that made hundreds of trees un-marketable.  However with monitoring and early detection, growers can control this disease.

Fir broom rust gets its name from the proliferation of shoots on affected fir stem ends, which leads to broom-like growths. These growths may occur randomly anywhere on the tree but are most likely to show up around the base of the tree first.  Their appearance can disfigure landscape trees and leave Christmas trees unsalable.

The affected fir needles on the brooms are stunted and curled downward. An orange, rusty coloration (masses of spores) may be noticed on the lower needle surface during the growing season.  These fungus-infected needles are shed during the fall and winter.  In the spring new needles grow from the infected shoots which are also stunted and curled.

Only true firs (Abies sp) are affected by this disease, including Fraser fir (Abies fraseri), balsam fir (A. balsamea), white fir (A. concolor) and grand fir (A. grandis). The Douglas fir (Pseudotsuga menziesii) is not susceptible.

The fungus that causes this disease (Melampsorella caryophyllacearum) also infects chickweeds.  In fact, for the fungus to complete its life cycle, it must move from chickweed to fir and back.  Both the common (Cerastium vulgatum) and mouseear (Stellaria media) chickweeds may be infected by the fir- broom rust fungus.

In the spring, fungal spores produced on infected chickweed are carried on air and can infect newly emerging stems and needles of fir trees.  The infected fir branches do not show symptoms until the beginning of the next growing season when infected shoots will emerge from these branches.  The spores from those infected shoots infect chickweed, continuing the cycle.  However, once infected, branches remain infected even without chickweed present.

To break the life-cycle and control the spread of this disease, eradicating the chickweed is essential.  Commercial growers should look for chickweed in the groundcover, between the rows and throughout the planting so it can be controlled where necessary.  The spores of this fungus may also move short distances into the field from chickweed in nearby hedgerows and vacant land so these areas should also be checked.  If chickweed is present in areas where it cannot be controlled, consider growing a tree species other than firs in these areas.

Pruning the affected branches of the fir trees back to the healthy portion will be helpful.  It is important to remember that those “brooms” that are missed will grow into bigger brooms each year and continue to produce spores.  So even after a grower controls chickweed they may still notice the symptoms from these missed brooms that become more noticeable each year.

At this point there is no information available on the effectiveness of fungicides for control of this disease.

The above information is available in factsheet form here: Fir Broom Rust, 2010, 230k pdf file

Greenhouse Disease Preview, 2010

Margery Daughtrey, Dept of Plant Pathology, Cornell University, Long Island Horticultural Research and Extension Center

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Based on past growing seasons some greenhouse diseases to watch for include:

Botrytis blight

Gray mold caused by Botrytis spp. can be found on all plants.  Be especially careful with bacopa, osteospermum, angelonia, lisianthus, snapdragon, dahlia, fuchsia and geranium.  Avoid excess leaf wetness or excess nitrogen fertilizer. Keep calcium levels up.  Remove dead plants or plant parts.  Keep plants’ lower leaves from sitting on wet surfaces.  Treat susceptible plants with fungicides as needed.

Fungal leaf spots and anthracnoses

Watch for Cercospora leaf spot on pansy and Colletotrichum anthracnose disease on leaves and stems on osteospermum and lupine.  Scout for first symptoms of these diseases and begin treatment promptly.  Control by watering early, reducing leaf wetness duration, spacing plants, removing badly spotted plants and through cultivar choices.

Downy mildews

Seen on coleus, pansy, argyranthemum, strawflower, iberis, veronica, geum, agastache, lamium, geranium, coreopsis, rudbeckia (cv. Goldsturm, in particular). High humidity favors this disease: keep plants spaced.  Note that related plants may share the same downy mildew pathogen, e.g. agastache is susceptible to the new coleus downy mildew.

Viruses

The most common virus on many greenhouse annuals is Impatiens necrotic spot virus (INSV).  The symptoms of this thrips-spread virus vary depending on the host plant.  Look for ring-like spots, spots with a concentric circle pattern, or round dead spots — any of these can be symptoms of INSV.  Alternanthera mosaic virus is seen on portulaca and angelonia; Angelonia mosaic virus on angelonia; and Coleus vein necrosis virus on coleus.  Viruses of perennials include Tomato spotted wilt virus (TSWV), INSV, both thrips-transmitted; Tobacco rattle virus (TRV) on anemone, hosta and epimedium; and Hosta virus X (HVX) which is common in cultivars Gold Edger, Gold Standard, Golden Tiara and Sum and Substance. There are now convenient test strips available for HVX as well as many other virus diseases.

Pythium and Phytophthora

Avoid overwatering, poor drainage, deep transplanting, or overfertilization especially with snapdragon, lavender, mums, and poinsettias.

For chemical control details (NY State):

Cornell Guide for the Integrated Management of Greenhouse Floral Crops

Pest Management Guide for the Production and Maintenance of Herbaceous Perennials

For illustrations of diseases on perennials:  Diseases of Herbaceous Perennials is available now from APS PRESS.

Biocontrol for Western Flower Thrips

Dan Gilrein, Cornell Cooperative Extension of Suffolk County

 

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Interest is increasing in the use of biologicals to control western flower thrips due to the suspected resistance of these insects to spinosad (Conserve).  Using any biocontrol takes commitment and some trial and error to learn how it will work at your greenhouse, but here are the basics.

Thrips Biocontrol Options (probably best used in a combination)

  • Hypoaspis mites for thrips pupae in the soil or media
  • Cucumeris (Neoseiulus cucumeris) predatory mites on foliage for younger thrips stages
  • Orius (minute pirate bugs) for all thrips stages on the plants. Orius may need supplemental lighting in the winter and performs best during the late spring through early fall. It also benefits from a supplemental pollen source: ‘Black Pearl’ ornamental pepper is commonly used but other peppers with abundant flowers or plants with pollen may also work.

Monitoring, sanitation and other usual thrips management strategies are especially important; check with biocontrol suppliers on release rates and with BioBest or Koppert’s Side Effects page for information on compatibility with insecticides and fungicides.

For a more complete look at thrips control, see Managing Thrips in the Summer 2008 issue of this newsletter.

and for up-to-date pest control information see the Cornell Guide for the Integrated Management of Greenhouse Floral Crops

Pest Management through Greenhouse Sanitation: Starting with the basics

Betsy Lamb, NYS IPM  eml38@cornell.edu

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Much of using greenhouse sanitation for managing disease, insect and weed pests is common sense.  Finding a way to fit it into your production system is sometimes the hard part – making it such a part of how you grow plants that you don’t even have to think about it.  As Dr. P. Allen Hammer said in his November ’09 Grower Talks article, sanitation begins with attitude – if clean is encouraged, clean becomes the norm.  So, start with the basics and add a few new procedures at a time until they become habit.

Think about what you are trying to control

Large populations of insects, big lesions on plant leaves, or weeds sticking up through the benches are horrifying but easy to spot.  But you need to consider the less obvious stages of the pests as well.  Disease spores are dust sized, weed seeds can be small, and some insect stages live in places where you can’t easily see them.  Most pests also form stages or structures that are meant to survive harsh conditions or long periods of time.  Pests can move with soil, with plants, and with pots, or find ways of hiding in structures and equipment.

Avoid points of contamination

It’s easy to pick up and spread something you can’t see.  Hose ends that hit the floor can pick up diseases and spread them to the next pot watered.  Tools used in making cuttings or cutting back plants have direct contact with a plant wound so must be dipped in alcohol or a disinfectant frequently.  Reused pots, sometimes even ones you have washed, can have disease spores on them ready to infect new plants. Your hands and feet go with you everywhere and you can move virus particles or weed seeds from place to place without ever noticing it.

Clean up as you go

In the busy season, it is easy to feel that you just don’t have time for sanitation.  However, in the long run, keeping things clean may save you time in later pest management.  Put any crop debris – dropped leaves, trimmings, sick plants – into a covered bin or a bag that can be closed.  Cover the container as you carry it out of the greenhouse so insect or disease hitch-hikers don’t jump out.  Be meticulous about getting rid of sick or infested plants and scouting around them to make sure what they have hasn’t spread.  Assume that anything that hits the floor needs to be tossed or disinfected.  Remove weeds in the greenhouse as soon, and as much, as possible.  Keep the area outside the greenhouse mowed or mulched 30-35 feet from the house to prevent weeds seeds from coming inside.

Keep your storage area clean

Almost all greenhouses have that area where things get stuck – too big or bulky to store easily, or you don’t need them that often, etc.  It’s easy for these areas to be ignored when you are thinking about sanitation.  However, dust-carried disease organisms, weed seeds, and flying insects can make it into those spaces, too.  If there is light, water and soil, weeds can grow and harbor a population of insects or disease.  Cover your pallets of media with a tarp to keep fungus gnats from finding a home through holes in the bags.  Make sure pots and flats are stored in their boxes or covered so disease spores don’t contaminate them before you use them.  And keep clean pots and media away from used pots and media.

Find time for the bigger jobs

For some sanitation jobs, you really need an empty greenhouse.  Disinfecting benches, floors and the greenhouse structure is more efficient and less likely to spread pests if there are no plants in the way.  Most chemical weed control products require that no plants are present.  Perhaps you can empty one house at a time and clean it, then move plants back in to create another empty house.  If you have a down season, do your cleaning earlier than later.  It is tempting to wait until it is time to fill the house again – and you definitely deserve a vacation.  However, weeds will have produced more seed, diseases and insects may have found weed hosts and spread, and those survival structures that are harder to kill may have formed.  Clean your floors first as dust can fly up onto the benches.  Consider redoing benches in wire or a non-porous material if you have any wood benches.  Fix any drainage issues to prevent puddles from forming.  Add, or clean accumulated soil off of, weed fabric on soil or gravel floors to reduce weed problems.

Reading a list of suggested sanitation practices is like looking at a long list of New Year’s resolutions – so daunting that none are accomplished.  So choose one practice you haven’t tried yet and see how it fits into your production system.  Then add another, and another . . . .

Late Blight of Tomato

Brian Eshenaur, NYSIPM,  bce1@cornell.edu and Betsy Lamb, NYS IPM  eml38@cornell.edu

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“Yes, everyone had that problem.”

“No, it’s not your fault.”

“Yes, you can grow tomatoes there again.”

These statements, displayed on a large sign were one garden center’s solution to the frequent questions during the height of last year’s late blight epidemic.  It is a complex issue but those three declarations bring main points home and getting that information out to consumers will be important this year in order for growers to help customers succeed.

Two factors came together to make it a devastating year for tomato gardens in 2009:  

Early Arrival of the Pathogen

Normally if the late blight pathogen (Phytophthora infestans) arrives at all, it gets to the northeast late in the season.  Since this pathogen doesn’t overwinter on tomato debris in the north it needs to travel from southern climates where tomatoes and potatoes can survive year round.  Air currents and summer storms from the South bring it here in most seasons.  Last year however it was reported to be brought up early from the South in infested tomato transplants.  Once there were spores in the air it spread throughout the region reaching backyard gardens everywhere in NY.

The Cool Rainy Weather

The unseasonably cool and wet summer last year provided perfect conditions for the late blight pathogen to flourish.  This organism is a “water mold” and requires moisture on the foliage to infect new plants.  The cool weather also not only enhanced the spread, it also kept the foliage from drying out, further encouraging disease. 

Steps to help prevent this disease in 2010:

Destroy any potato tubers from last year

Late blight can also infect potato plants.  Since potato tubers have the potential to survive the winter underground they should be destroyed to prevent carrying over the disease.  If you see any volunteer potatoes popping up in the garden this year dig them up and bag the plants and send them to the landfill.  If planting potatoes be sure to start with clean seed pieces.

Start with healthy tomato plants

Consumers should look closely at their plants and choose transplants that have no signs of disease.  Since this disease does not survive on seeds, locally grown tomatoes should be disease free.  While there are some resistant varieties, like Mountain Magic and Plum Regal, the seed is not yet widely available.

Don’t worry about the soil

Late blight is not known survive in the soil in the Northeast.  While we recommend not planting the same crop in the same place year after year for some other diseases, healthy transplants planted in the same location will not be infected by late blight from the soil.  Also, well-composted (reaching 115 F) plant material does not spread late blight.  Stakes and tomato cages also will not spread late blight.

Consider protecting plants if it pops up again

If the conditions are right and the disease is in the air again some gardeners are planning to use fungicides to protect their prize tomato plants.  They should monitor and start at the first sign of disease and know that these products can protect against new infections but will not cure blighted portions.

Cornell IPM Team for Production Ornamentals
Betsy Lamb
State Coordinator for Ornamental Crops IPM
Ithaca, NY, eml38@cornell.edu
 
Brian Eshenaur
Western New York Specialist
Rochester NY bce1@cornell.edu
Disclaimer: Pesticide recommendations are for informational purposes only and manufacturers' recommendations change. Read the manufacturers' instructions carefully before use. Cornell Cooperative Extension and Cornell University assume no responsibility for the use of any pesticide or chemicals.
Some of the links provided are not maintained by Cornell Cooperative Extension and Cornell University. Cornell Cooperative Extension and Cornell University are not responsible for information on these websites. They are included for information purposes only and no endorsement by Cornell Cooperative Extension or Cornell University is implied.
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