Viburnum Leaf Browning Probably NOT Spider Mites

What’s happening to my Spring Bouquet (Viburnum Tinus)?  It bloomed beautifully in the Spring for several years (including this past Spring), but many of the leaves are turning brown, and appear to be burnt.  I didn’t see any evidence of spider mites or other pests.  I checked the drippers and it is getting sufficient water.  Is this damage caused by Fire Blight, Spider Mites, or something else?  I was planning to spray it with Bayer 3 in 1 Insect, Disease, & Mite Control (which contains Imidacloprid, Tau-fuvalinate &Tebuconazole). .

Any assistance would be appreciated.

A. You are correct to inspector for spider mites this time of year. We usually see them when weather has been hot and dry. Spider mites can be a problem even if we don't see webbing. Webbing isn't always present. Spider mites love dusty leaves so washing the leaves off with water after windy weather is a good idea.

 

Two spotted spider mite. Actutally the size of this period......

That being said, I don't see spider mites as a problem in the pictures you sent to me. Spider mites don't live very long so their dead bodies leave behind kind of a dusty appearance to the leaves. I also use a hand lens and look for their tiny eggs which are round translucent balls. Finally I take a branch and slap it against a white piece of paper. I look for tiny crawly things about the size of the period at the end of the sentence.

 

This is spider mite webbing but doesn't always happen

I don't think you have them. I think this problem is water related. Either the plants are watered too often, they are not given enough water when they are watered or they are given too much water. You didn't tell me how often you water but I think you are may be watering too often. That's my guess. Root suffocation or rot is relatively common on viburnum unfortunately.

Water less often.  When you water, give them a lot Of water at one time and then hold off until they need it again. Never water these every day. At the very least you should be able to water them every other day. Maybe even every 3rd day.

Increase the number and size of the emitters. The easiest way to Give them more water is to increase the number of emitters and the size of these emitters to this plant. For example, if this plant has 2 emitters Watering it, increase it to 4 emitters. If this plant has 2 gallon per hour emitters, change them to 4 gallon per hour emitters.

it is better to give them too much water all at once and then wait than it is to water them every day.

Improve drainage. Soils that have little amendment in them to improve the drainage get worse over time. This is because the organics in the soil decomposes and disappears. This causes the soil's to collapse and drain poorly. This causes poor drainage and leaves water around the roots and suffocates them.

Get a 1 inch diameter or larger auger that can attach to a drill. Make sure this auger is at least 18 inches long. Drill 8 to 10 of these holes within 12 inches of this plant without hitting your irrigation lines. Leave these holes open and drill more of them when they collapse or fill them with compost to help keep them open. You are creating a French drain or a sump, sometimes called vertical mulching. This helps move water away from the roots that might be suffocating them.

Replace the rock mulch with wood chips. Wood chip mulch on the surface of the soil decomposes and improves the surface layer of the soil. Rock mulch doesn't. It actually makes the soil worse for drainage.