Plant and Pest Problems Diagnosis
Via the Computer and Internet
Robert Berghage, Assistant Professor of Horticulture

The internet is finally beginning to live up to it's promise. There is now an increasing amount of useful information on the WWW that is available to anyone with a connection. Green industry professionals can find everything from basic fact sheets on plant problems to pesticide recirtification meeting announcements, to on-line training programs, to unique business opportunities.

For most green industries users the internet can provide basic information and a connection to fellow professionals through e-mail and list servers. This later function can be very helpful in diagnosing problems since you can tap experts from around the globe. Long term many green industry businesses will conduct more and more commerce over the web.

Finding the information you want can be the most frustrating part of using the internet. One of the best ways to find things is through links from pages that you like. The following are a few starting points for you to use.

Penn State

• Horticulture: http://garden.cas.psu.edu
• Trial Gardens: http://garden.cas.psu.edu/garden/index.html
• Plant Disease Facts:http://www.cas.psu.edu/docs/CASDEPT/PLANT/ext/fact.html
• Pesticide Education Program: http://www.pested.psu.edu
• PA IPM Website: http://www.cas.psu.edu/docs/casdept/ipm/index.html
• Pen Pages: http://www.penpages.psu.edu
• World Campus: http://www.worldcampus.psu.edu/pub/index.shtml

PDA

• Bureau of Plant Industry: http://www.state.pa.us/PA_Exec/Agriculture/plant_industry.htm

Other Sites

• National IPM Homepage: http://www.reeusda.gov/nipmn/
• Northeast IPM Network: http://www.nysaes.cornell.edu/ipmnet/index.html
• Cornell IPM Ornamentals and Turf: http://nysaes.cornell.edu:80/ipmnet/ny/ornamentals/
• Cornell Pesticide Education Program: http://pmep.cce.cornell.edu/
• Biological Control: http://www.nysaes.cornell.edu:80/ent/biocontrol/

Nursery and Landscape Weed Control
Part I: Basics
Jim Sellmer

This is the time of year where most nurseries, garden centers, and landscapers are spread thin with plant deliveries, sales, and installations. Thinking about weed control, although important, is not the first thing on the mind. Even so, the well-organized grower took a few days off during deer season and applied a postemergence herbicide to control the tough perennials such as Canada thistle. In addition, they applied a preemergence application on to control winter annuals. That sounded like a plan and that's where it all begins.

Taking time to develop a plan reduces the time, money, and energy you expend on the controlling weeds during the season. Scheduling your activities and following through with them will insure that things are done on time and that you are not putting out fires at the busiest of times.

What's your plan and weed control program? Anyone growing or maintaining ornamental plants should have a weed control program. This means planning how to control weeds in a crop before and after planting.

A Good Program Has Three Parts:

1. Eliminate the weeds in and around the growing area before planting. This includes killing seeds and vegetative parts. You have the greatest latitude in choosing and using weed control products before planting than you will at anytime after planting. Killing the perennial weeds is a necessity since they are not controlled by mulches, preemergence herbicides, or cultivation. In fact, cultivation will only propagate them and make your job that much more difficult. In addition, weed control should include the surrounding area. Your effort to control weeds in the growing area will be less effective if a source of weed seed is constantly present nearby.
2. Prevent weed growth in and around the growing area. Mulches and preemergence herbicides can control germinating weed seed, but will not prevent established perennial weeds from growing. If a weed seed source is near by then you will likely have weed seeds blowing in and germinating in the mulch. Preemergence herbicides and hand weeding can be used to control those weeds, but the weed seed source must be dealt with to reduce future infestations.
3. Eliminate weeds as they appear. Since few preventative methods provide total control, hand weeding, cultivation, or careful spot treating with a postemergence herbicide usually are necessary.

Accepting that weed control is an ongoing and permanent part of growing ornamental plants is the first step in developing a sane and manageable weed control program. Recognizing that all three stages of the program are necessary to maintaining control will insure a balanced program and reduce misconceptions on what a weed control program can do.

Several Points Should Be Considered In Developing Your Weed Control Program:

1. In most situations, one application of a preemergence herbicide at the recommended rate will NOT provide season-long control. Repeat applications will be needed. In addition, disturbing the site after applying the herbicide will result in sites not protected by the preemergence barrier. Growers who get season-long control from an application probably are applying herbicide at too high a rate and may be stunting the growth of their crop.
2. No one preemergence herbicide controls all weeds. Some control broadleaved weeds better than grasses, while others control grasses better than broadleaved weeds. Some postemergence herbicides control most weeds, but their use is restricted in established plantings.
3. If one type of weed is controlled and another type in the same areas is not, the uncontrolled one will eventually cover the area. To get preemergence control of a broad spectrum of weeds, combinations of herbicides should be used. When more than one application is made in a season, herbicides should be alternated from one application to the next.
4. Growers who spend the time and money to make an area weed-free should take measures to prevent weed regrowth by mulching or applying and preemergence herbicide to the area.

Points about Preemergence Herbicides:

1. Preemergence herbicides generally do not control established perennial weeds, even if applied prior to their emergence, or annual weeds that have germinated and begun to grow.
2. Tillage prior to application allows better penetration and distribution of the herbicide in the soil. Application to moist soils is preferable to dry soils. Following application, all of the preemergence herbicides must be activated by 0.5 to 1 inch of rainfall or irrigation or must be mechanically incorporated to become fully effective.
3. It is preferable that herbicides not be applied to new transplants until the soil is settled by irrigation or rainfall and there are no cracks in the soil leading to roots of ornamentals. However, since many weed seeds germinate early in the season, it is also important to make an herbicide application as soon as possible after planting.
4. Apply granular products to dry foliage. Granules that stick to wet foliage may cause injury. Do not apply granular herbicides to herbaceous plants with whorls of leaves that channel granules to a growing point at their base or the plant may be severely injured.
5. Most preemergence herbicides such as Casoron, Treflan, and Devrinol are more effective and last longer when placed under an organic mulch. The exceptions are Goal, Goal containing products like Rout, OH2, and Regal O-O, and Ronstar, which should be placed on top of mulches because they need sunlight to be active.
6. Most of the preemergence herbicides can be safely applied over the top of many ornamentals, even during active growth. There are some exceptions. Read the label before applying any herbicides.
7. Applying the same herbicide time after time can result in a buildup of weeds that are resistant to the herbicide. Use combinations of herbicides and periodically switch the herbicides used.
8. Remember, no one preemergence herbicide controls all weeds.

Points About Postemergence Herbicides:

1. Intact foliage is needed to absorb the chemical, and intact foliage and root systems are needed for complete translocation. Do not mow or cultivate for at least 2 weeks prior to application or 5 to 7 days following application.
2. Healthy, actively growing weeds are controlled faster and more thoroughly than plants under stress from drought or pest problems. Injury symptoms from contact herbicides develop quickly (from hours to a day or two). Injury symptoms from the translocated products may take 7 to 14 days to develop.
3. Control of perennial weeds requires higher rates of application than control of annual weeds.
4. A surfactant may be needed to improve coverage of the foliage and absorption into the weeds. Some products include surfactant with them; for others' one must be added. A typical amount would be 0.25% v/v (volume per volume). To make a 0.25% solution, add 2 teaspoons to 1 gallon or 1 pint to 50 gallons. The exact amount to add will vary with the brand of the surfactant. Read the label of the surfactant to determine the exact amount needed.

These are just a few tips to get you thinking about developing a manageable and timely weed control program. Next month we will look at weed control recommendations for specific growing situations. Until then, consult the PSU extension publication Controlling Weeds in Nursery and Landscape Plantings by Larry Kuhns, Tracey Harpster, Mary Ann Rose, and Scott Guiser. This publication is available from your county extension office or the Publications Distribution Center, 112 Agricultural Admin. Building, University Park, PA 16802. For ordering information call 814-865-6713.

A Note on Purple Loosestrife

At a recent Pennsylvania Department of Ag (PDA) Inservice Training, Will Mountain (Botanist) announced that the Bureau of Plant Industry will be requesting the Noxious Weed Control Committee to place additional weeds on the Noxious Weed List. The plants effected will be Lythrum virgatum and any cultivars of L. virgatum and L. salicaria.

The ability for L. salicaria and L. virgatum to intercross has made identification and regulation difficult. Controlling the spread of purple loosestrife has been exacerbated by the mistaken belief that the ornamental cultivars of Lythrum are sterile. Although most cultivars are self-sterile (incapable of self pollination) research has shown that the self sterile barrier is leaky and that cross pollination via bees and wasps can occur and is effective. In addition, the native, non-invasive loosestrife (L. alatum) has also been used as a breeding source for some purple loosestrife cultivars. This heightens the potential for adaptive characteristics of L. alatum to be combined with the aggressive characteristics of naturally occurring and ornamental varieties of loosestrife. Evidence suggests this has already occurred.

For these reasons, PDA will ask the Noxious Weed Control Committee to consider any non-native Lythrum species including L. salicaria, L. virgatum, and their cultivars to be added to the noxious weed list. The Bureau of Plant Industry is advising greenhouses, nurseries, and garden centers not to propagate or buy purple loosestrife cultivars once their present loosestrife inventory is exhausted.

Information provided by Rob Berghage and Jim Sellmer Penn State Department of Horticulture, Ornamental Horticulture Extension Specialist, 103 Tyson Building, University Park, PA 16802, (814) 863-2571

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