SPRAYING TREES FOR PESTS AND DISEASES

Spraying was used for many years to treat many pests and diseases.  Now, sprays are seldom useful for insects because systemic controls are possible without harming beneficial insects.  Sprays are necessary for some fungal diseases. 

Unfortunately there are many companies that "sell spray" and do spraying indiscriminately.  Those companies seem to suggest that spraying can cure all problems.  The consumer is at their mercy, regarding them as the "experts" and thus trusting the recommendations they give.  Spraying should be done only for specific problems, only if the benefits outweigh the negative effects and only using the specific technique and with the timing demanded by the problem at hand.

We rarely spray anything other than fungal diseases.  Occasionally we will spray miticide, but when we do it is NEVER mixed with an insecticide.  

WHEN SHOULD SPRAYING BE EMPLOYED?

1.  The pest or disease must be specifically identified.  General cover sprays of pesticide mixes are never a good idea.  The technique, timing, and type of spray depends on exactly what is being treated.  Michigan law requires that commercial pesticide applicators inform the customer of what specific pest or disease the treatment is targeting.

2.  The damage or potential damage to the tree must be sufficient to warrant spraying of toxic chemicals.  If the problem is more cosmetic or nuisance, then an informed decision should be made as to whether spraying is warranted.

3.  The timing should be right.  The life cycle of most pests and diseases give only a small window of opportunity for spray control  Spraying at other times is not effective and could actually worsen the problem (see Cottony Maple Scale on scale treatment page).  A reputable spray company will inform the consumer if the treatment window has passed, as it often has when homeowners call.  Unfortunately, many "spray sellers" do not even know the life cycle of common pests and diseases and are not motivated to tell the consumer that sprays are not needed or would not be beneficial.

There are some diseases that require a series of sprays for control.  When that is the case, timing is critical for each application in the series.  Many spraying companies time their "treatments" by the calendar and not by the life cycle of the organism to be controlled.  They apply combinations of products in a shotgun, "one size fits all" approach that is not scientifically sound and can cause as many problems as it is intended to treat.

The "spray sellers" often say that theirs is a "preventive" approach, suggesting that applying an insecticide and a fungicide and maybe a miticide several times will prevent any problems that could arise.  That is akin to a doctor giving a patient pills for several different diseases and instructing them to take the pills regularly just in case the patient is prone to those diseases.  The adverse effects would likely outweigh any potential beneficial effects.

WHAT ABOUT "DORMANT OIL" SPRAYS?

We are often asked about dormant oil sprays.  They are still routinely applied by many companies and can be beneficial in some cases.  We abandoned the use of oil sprays many years ago for a number of reasons:

1.  Dormant oil sprays are promoted as a less toxic alternative to the use of insecticides and miticides.  In fact, they are less likely to harm beneficial insects and if applied properly, with correct timing and technique can help to control scale insects and possibly cool season mites.  They may also be effective for some adelgids.  Our experience has been that even with good equipment and good technique, control has been limited and disappointing to us and our customers.

2.  Oils work by "smothering" the insects or mites.  In order for this to happen, a continuous layer of oil must be applied to all the plant tissues and must persist for long enough to kill the pest.  The optimal conditions for this to happen include a specific temperature range at the time of application, correct humidity conditions and the timing has to be right to contact the pest during a vulnerable stage of its life cycle.

3.  Oils can cause damage to some evergreens and some tissues and young foliage on deciduous trees.  In many cases, this damage is worse than the damage of the pest being treated.

4.  Oils can damage surfaces of houses, lawn furniture, vehicles, swing sets, etc. and it is difficult to keep the spray off of those surfaces when spraying even smaller trees.

5.  It is virtually impossible to get adequate coverage of large trees for oils to work, even with excellent equipment and experienced applicators.

We have found that we can achieve excellent control of soft scale insects on very large trees with trunk injection of insecticides. There is long term control, no adverse effects on beneficial insects, and no environmental toxicity. 

Mites can be treated with specific miticides.  Adelgids can be treated with systemic, soil injected or drenched insecticides that have very low toxicity and do not damage surfaces or healthy foliage.

SPRAY SERIES FOR FUNGUS DISEASE CONTROL

Several diseases of trees are treatable with sprays.  Fungal diseases of evergreens include tip blight and needlecast diseases.  Scab on crabapple trees is also treatable.  Many fungal diseases of deciduous trees are difficult to treat with sprays and may respond better to trunk injections.  Most of the leaf fungi (anthracnose, leaf spots and leaf blotches)  require no treatment at all. 

Treatable diseases require a series of specific fungicide sprays applied with very good technique and with fungicides labelled for the problem at hand.  Many "spray sellers" apply fungicide by adding it to a cover spray along with insecticide.  In many cases it is the wrong fungicide and is applied at the wrong time, usually too late in the spring. 

Most fungal diseases in Michigan require an early spray in April, followed by two or more additional sprays.  Crabapple scab and Tip blight on pines must have a spray as buds are opening.

Needlecast diseases require sprays in mid-May and mid-June and do not  respond to common fungicides like Clearys 3336 and Bannermaxx.  Blue spruce Rhizosphaera needlecast will respond to Daconil (chlorothalonil) or copper fungicides and Pine Dothistroma needlecast requires copper fungicides (Junction, Kocide, Cupro).