Natural Resources

Staff and volunteers with the Prince William Cooperative Extension’s Environment and Natural Resources program provide educational programs for individuals and business to implement sound practices producing aesthetically pleasing landscapes that have minimal negative impacts on the environment. Programs include: 

Master Gardeners The Teaching Garden
​​Publications & Additional Resources Horticulture Classes
Stormwater Management
Landscaping Guide for HOA's Horticulture Speaker Request
New and Emerging Pests BEST Lawns
​​Championship & Historic Tree Registry Pesticide Training Page​
Audubon at Home​ Commercial Landscaping Classes
​Virginia Household Water Quality Program ​Other Regional Classes



Seasonal Tips

The Environment and Natural Resources team and Master Gardener Volunteers of Virginia Cooperative Extension, answer many questions throughout the year.  Below are some of our most frequently asked questions for this time of year.

If you have additional questions, give our Extension Horticultural Help Desk a call at 703-792-7747
or email us at

Horticultural Tips 
Trees and shrubs:
Drought can weaken trees over time.  With continuing droughty summers, many trees are starting to see the results of under watering in past years.  Weakened trees become more prone to disease and insect damage.  Trees and shrubs need an inch of water a week under the canopy out at least to the drip line.  Watering should be deep and infrequent.  Because some soils can’t handle one inch of water all at once with causing run off, you may have to apply water every 3-4 days to get one inch’s worth of water in a week.
Periods of extreme heat, with or without wind, may prevent fruit set on Peppers.
Mature tomato plants suffering from such stress may produce small fruit, hold its fruit on the plant but not enlarge, or drop its flower blossoms.
If you have warm season turf, this is their time of year.  Adequate moisture is essential for their health and growth, but most warm season grass does not need to be watered in a home lawn setting.
If you have cool season turf, you have to make the decision to either water for the summer or let the grass go dormant.  If you choose to water to prevent dormancy, cool season turf needs 1 inch of water per week.  Dormant grass will lighten in color.  Most of the time, they can handle the extremes of summer and will re-green with autumn rains.  Dormant cool season turf can survive on ½ inch of water every 2-3 weeks during periods of exceptionally high temperatures.
Watering should be deep and infrequent.  Because some soils can’t handle one inch of water all at once with causing run off, you may have to apply water every 3-4 days to get one inch’s worth of water in a week.  Watering lightly every day is NOT good for your grass as it produces weak shallow roots.  Water should be done as early in the morning as possible.  This will lessen losses from evaporation and won’t encourage disease.  Make sure you’re mowing high for the summer.  That extra height makes a big difference in soil temperature and moisture retention.
If you lose grass to the summer or are looking for better drought tolerance in your grass, you may want to consider over seeding with more resistance grass varieties.  Contact our office for type and varieties recommendations.

 Weeds to Watch for:

Japanese Stiltgrass  (Microstegium vimineum) is a native of Asia, first appearing in the U.S. in 1919, spreading rapidly throughout the eastern U.S. It is shade tolerant a summer annual, most often found in moist, shady environments including forests, turf, ornamental beds, ditches and damp fields.  Japanese Stiltgrass has a fibrous root system, stems which are erect or reclining and roots at stem nodes. Its leaves are four (4) inches long and one half (.5) inches wide with a white mid-vein which divides the leaf into unequal halves. The seed head has 1 to 6 terminal spike branches. The seeds will germinate in late March to early April in the average year, which is before crabgrass. Flowering occurs in late September to early October in this region.
Control recommendations are to hand pull this weed before it flowers.  Where there is a sizeable stand of this then control is best accomplished with the use of properly applied pre- and post-emergent herbicides combined with mechanical removal.
Pre-emergent control of Japanese Stiltgrass can be started soon.  Remember the early germination of this weed, before crabgrass, and note the rainfall during this period. Control options are similar to that of crabgrass, start early and reapply in wet years.  
The best time to fight crabgrass is before it germinates. The first line of defense is a thick, healthy turf. Crabgrass does not compete well with a thick turf, but moves in very quickly in lawns that are a little thin, or have numerous bare spots. A big part of developing a healthy, weed resistant lawn is to mow high (2-3 inches) and practice fall fertilization. Fall fertilized lawns do not need a spring application, which will only promote excessive growth at the expense of root development, and feed spring weeds. However, if crabgrass is a yearly problem, then pre-emergent herbicides are recommended. There are several chemicals labeled for pre-emergent crabgrass control, and they all work. They have many different brand and trade names, but are often called ‘crabgrass preventers’. Some of the more common ingredients in crabgrass preventers include balan, dithiopyr, and pendimethalin, and again, they are sold under various trade names. The best time to treat is when the dogwoods are in bloom, which is mid-April in most areas. The old standard of using forsythia as a guide is no longer recommended. Crabgrass is an annual and needs warm soil for the seeds to germinate, so do not rely on forsythia, which often starts to bloom during the first warm spell in February. A problem for many homeowners is to find pre-emergent herbicides sold by themselves. Many stores only sell pre-emergents (crabgrass preventers) mixed with fertilizer. Again, the recommendation is to use fertilizer in the fall, and pre-emergent herbicides without fertilizer in spring. More stores are starting to carry pre-emergents, but they can still be hard to find. One more thing to remember is that most pre-emergents will also keep grass seed from germinating. If spring seeding and crabgrass control are in the schedule, a special product containing siduron, which is often sold as Tupersan, is recommended. It is a specialized pre-emergent that allows turf grass to germinate, but still prevents crabgrass. It is expensive, but well worth the cost.
This article was taken from the Bi-Weekly Updates series written by Chuck Hoysa Fauquier Extension Agent, Retired.  These are also available on the VMGA website.

If you have additional questions, give our Extension Horticultural Help Desk a call at 703-792-7747 or click here to send an e-mail to us. It’s not too late to participate in the BEST Lawns program.  For a $25 fee, we can measure and sample your lawn, develop a nutrient management plan tailored to your lawn and provide information to help improve the problems specific to your lawn.  For more information visit BEST Lawns on the Prince William County website.

While not complete, the following are diseases and insects that are more commonly found this time of year.  Contact the Extension office for help with diagnosis and control recommendations. 


Many insects are starting to appear in and around the house.  Virginia Tech has factsheets on many common insects.  VT Fact Sheets Insect ID or call our Horticultural Help Line for information on what's "bugging" you and the best and safest way to cure the problem.


Anthracnose:  Lesions are usually quite large and follow the veins of the leaf.  Trees may drop some affected foliage.  These diseases normally occur on large trees and do no permanent damage – practice good sanitation by cleaning up fallen leaves. You may choose to apply a preventive fungicide treatments next spring.  A certified pesticide applicator and certified arborist can make these treatments fore you.

Plants susceptible:  ash, maple, sycamore and oak trees.

Fireblight Caused by a bacteria.  The most typical symptom is branch die back from the tip down typically resembling a shepherd’s crook.  Affected branches usually start dying in mid-May or June.  Prune out dead branches about a foot below the dead tissue.  Sterilize pruning shears between cuts.  Plants susceptible:  cotoneaster, pyracantha, apples, pears and Bradford pears.

Juniper Tip Blight:  Characterized by dead branch tips in juniper plantings.  Two different fungi cause this blight.  Small outbreaks can be pruned out.  Fungicides are also an option.  The timing of the treatments depends on the causal fungus.  Blight caused by Phomopsis is treated in the spring.  Blight caused by Kabatina is treated in the fall.

Oak Leaf Blister:  The light green to yellow spots will turn dark brown or black later in the season.  This disease is primarily cosmetic and requires no action.

Rose rosette disease (RRD):  A disease believed to be caused by the recently identified Rose rosette virus, has been spreading through much of the wild rose population of the Midwestern, Southern, and Eastern United States for years. It has been confirmed in cultivated roses in Virginia and other states.

Virginia Cooperative Extension
Environment and Natural Resources
8033 Ashton Ave. Suite 105
Manassas VA 20109
703-792-6285 - e-mail
Virginia Cooperative Extension complies with the Americans with Disabilities Act. If you are a person with a disability and require auxiliary aids services or other accommodations for a workshop or meeting please discuss your accommodation needs at least five days prior to the event with Virginia Cooperative Extension 703-792-6289/TDD PC 1-800-828-1120