Summer Monsoon: High Temps + Increased Humidity = More Disease

This is the time of year, around mid summer, when we can expect an increase of the moisture content in our weather. Arizona has it worse. They, and New Mexico, frequently call it their “summer monsoon”. It accounts for 35 to 45% of the state's annual precipitation. In Mexico, it accounts for 60% of the annual rainfall in Sonora.

Cloud development typical of summer monsoons.

The summer monsoon is not well understood but we know that it moves inward from the Pacific Ocean because the land heats up faster than the Pacific Ocean. The monsoons mostly stop around the Phoenix area but we do see an increase in clouds building from the South and, more importantly, an increase in our relative humidity.

So why is this important? Because it causes an alteration in some plants susceptibility to diseases.

This all goes back to the plant disease triangle. The plant disease triangle was probably one of the most important concepts I was ever taught in plant pathology while in school. The disease triangle relates to a three-legged stool; each leg coinciding with an increased potential for disease development.

These three factors are: the predisposition of the plant to disease, the presence of the disease organism, and an environment that is conducive to the development of disease. When the summer monsoons come into play, all three of these legs of the stool become activated. Let me explain.

Plant disease triangle

Predisposition of the plant. Healthy plants normally ward, or can fend off, diseases. Just like us, the healthier we are, the better able we are to withstand diseases. The plants more susceptible to diseases are those that are weakened, in poor health, old, malnourished or in some way compromised. This is why I encourage you to feed your plants on a regular basis. This helps to maintain their health. As summer temperatures increase, plants have a reduced capacity to withstand diseases. The summer monsoon comes at a time when plants have been hit hard with high temperatures and are under a lot of stress.

Presence of the disease organism. We can make some assumptions. The assumption I like to make is that most common disease organisms are always present in our garden or landscape. Two factors that contribute to the possibility that a disease may become a problem are the amount of inoculum (that is the total amount of bad disease organism) present and the virulence (the strength) of that organism. If the disease is highly virulent, it will not require a lot of that organism to be present for the disease to occur. If there is a lot of inoculum present, the potential for disease is high.

Environment. The third factor is the physical environment surrounding the plant and the disease organism. Fungal diseases, our most common plant diseases, require a wet environment to prosper. Bacterial and viral diseases, less so. When the humidity increases, the moisture in the environment increases, and the propensity for diseases to occur increase. If the other two factors in this three-legged stool are leaning towards a disease problem, higher humidity may send it over the top.

The adage in plant disease control is to manage plants and their environment to minimize disease problems by considering all three legs of the stool. Eliminate one of the legs and the disease can be managed or controlled.

These summer monsoons come at a time when plants are under a lot of stress due to high temperatures, high light intensities, poor soils, poor irrigation practices and a host of other things. The disease organism is present. Count on it. They are there and ready for any opportunity that presents itself. Now, the summer monsoons come, increasing humidity. Our biggest disease problems will come from fungal diseases that prefer higher humidity, higher temperatures and plants that are susceptible.

Bug Sprays Commonly Kill Bark Scorpions

Q. I never saw a scorpion in 24 years here and now I have them on my property. This is upsetting to me since I only had to deal with Crickets and an occasional black roach. I did not want to get a pro exterminator but did not have a choice after finding 2 in my house. Can you tell me what attracts them and how they could have become a problem in this area?

Source for picture no longer available but not mine.

A. I hesitate a little bit when answering questions like this because it's a little bit out of my area. But yes, I have had a few people tell me they have had problems with scorpions in their homes and one boy I know of was stung. Stings are painful but rarely life threatening.

There is quite a bit of information out there on scorpions on the Internet and it is probably easier for me to just give you some links so you can read up on this critter.

I believe they enter homes mostly for food. They need very little water unlike roaches. And also unlike roaches they don't seem to congregate near sources of water such as laundry rooms, kitchen cupboards, bathrooms. 

I have heard rumors from people that they are hard to kill with pesticides. I have not found that to be true at all. I have found them to be very susceptible to many common bug sprays. 

 Insecticides that are used commercially for controlling scorpions are usually the synthetic pyrethroids. Fortunately these insecticides are also used to control roaches, crickets and spiders; most of their food sources in the home. Most of the synthetic pyrethroids used for insect control will have the active ingredient listed on the label ending with the suffix -thrin.

If you are looking for a chemical to use then I would select a pesticide that is labeled to use inside the home and has as an active ingredient a chemical ending in –thrin. Examples are Resmethrin, Permethrin, etc. I recently saw a pesticide on a shelf in Ace Hardware actually labeled for scorpion control. It contained a -thrin.

Follow the label directions precisely. A chemical barrier can be sprayed around the outside of the home at soil level and 12 inches above it all around the foundation. Inside the home, please read and follow the label. 

Scorpions usually come out at night. They can be detected with a black light because they fluoresce or shine when using a black light and shining it on them. They can climb walls, rough vertical surfaces and trunks of trees. They come on at night looking for food and usually hide during the day. Outside they can be in woodpiles, rock piles, anywhere they can find food. Frequently they are on the underside of things since they seem to like to be upside down. Probably a better position to be in when lying in wait for their prey.

http://en.wikipedia.org/wiki/Arizona_bark_scorpion

http://www.scorpionworlds.com/arizona-bark-scorpion/

http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm266515.htm

Viragrow Delivers! : Pepper Leaves Curling. Bugs Again!

Viragrow Delivers! : Pepper Leaves Curling. Bugs Again!: Leaves curling on pepper. Typical pepper leaf curled on the plant. Flip leaf over and we see evidence of aphids feeding. We see ...

Olive Tree Dropping Leaves, Leaves Yellowing

Q. I have an olive tree that is approximately 20 years old.  It loses leaves year round and in excess. Some leaves are yellow but most are green. It is planted in lawn. It is watered twice a day for a total of 10 minutes. What can I do to stop this excessive leaf loss?

A. Olive trees are evergreen so they will constantly lose leaves during the year. The heaviest leaf fall should be in the spring during new growth or during the winter if there is a hard freeze.

Not the readers olive tree.

            These trees are tremendously versatile and can withstand droughty conditions as well as fairly wet conditions. They can handle a wide range of soil types.

            They handle abusive pruning techniques. That is the main reason they are used here.

They are resilient and respond quickly after being damaged, either by humans or the environment, as long as they get enough water. Being planted in lawn, I would assume they are getting plenty of water.

            If the canopy of the tree is beginning to thin, it is because there is not enough new growth to replace the leaf drop. If the lawn is fescue in good condition and well-managed, it should be receiving plenty of water. If the lawn is bermudagrass, then that is a different story.

            Fescue lawns require frequent irrigations because of their shallow roots compared to trees. Olive trees are deeper rooted and require water less often but with higher volumes so the entire root system is irrigated. Growing in bermudagrass they might require supplemental water besides lawn irrigation.

root knot nematode on tree roots. this is mulberry but it will be similar.

            Olive trees growing in lawns usually develop roots closer to the soil surface than without grass because of the shallow lawn irrigations. I would not think leaf drop would be a big problem unless your soils stay wet between irrigations.

            Normally soils that stay wet are described as heavier soils and have a high percentage of clay. This should not be a problem in sandier soils.

            Olive trees have few pest problems but one that can cause excessive leaf drop and stunting of growth are nematodes. The usual nematode is the root knot nematode, the same one that damages many vegetables, fruit trees, ornamental trees and shrubs.

            The only way to find out if this little guy has invaded the roots of your tree is to dig down through the grass, find some olive roots, and inspect them for little knots or round balls growing along the length of one or two-year-old roots.

            Even if you find them there, there is nothing really you can do to get rid of them. The recommendation would be to fertilize and water the tree separately from the lawn to encourage more growth. More growth helps to cancel out the stunting effects from the nematodes.

            Have someone knowledgeable about pruning do some selective limb removal throughout the tree canopy. By removing some of the unnecessary limbs, more growth will be forced into the remaining limbs and will provide better light penetration into the canopy.

Reviving Crepe Myrtle After Neglect

Crepe myrtle with annual fertilizer applications

Q. I inherited an established crepe or crape myrtle tree when we moved into a bank-owned vacant home two years ago.  The landscaping was pretty distressed.  I replaced the rock mulch with bark and the drip system seems to be working fine.  The tips of the leaves are dry and brittle and it blooms very little.

A. You are probably going to have to give this crepe myrtle a jumpstart. It is good you put down a wood mulch with this type of tree. I hope this is wood and not bark mulch.

            Since it is summer now you want it to push some new growth so you can see the tree’s strengths. Fertilizer is okay to apply now to trees and shrubs.

            Use a normal tree and shrub fertilizer and apply it a foot or two away from the trunk and close to its source or sources of water. Water it in with a hose.

            Construct a moat or a doughnut around the trunk of the tree at least 4 feet in diameter and 4 inches tall. This is nothing more than an irrigation basin to hold water. Fill this basin with water from a hose once a week for the next four weeks. Let your irrigation system run normally during this time.

Crepe myrtle trunk and bark

            Let irrigations push the fertilizer into the root area of the soil over the next couple of weeks. At the same time, add an iron chelate along with the fertilizer. The best iron chelate is iron EDDHA. You can find it in most nurseries now.

            When the weather cools off in the fall, around September, spray the foliage with Miracle Gro fertilizer used for the promotion of flowering. Try using a hose end fertilizer applicator so you can get it to spray that high.

            If you can't spray that high, apply it to the soil and water it in.

            Next spring start pruning out the deadwood in the canopy. Don't climb in the tree, but rather I would use a ladder. This is time-consuming because you will be cutting a lot of tiny branches along with some larger ones. Basically you are thinning out the canopy and getting rid of branches on top of each other or crossing each other.

            I question if your tree is getting enough water. If it is a sizeable tree it will require 30 or more gallons during each watering. You will have to look at your irrigation emitters and the time on your irrigation valve to figure this out.

Cut Lantana Back in February, Water and Fertilizer for Good Growth

Lantana regrowth when cut back to about 2 inches in February

Q. Why does Lantana grow and bloom with wild abandon everywhere but in my yard.  These plants are two years old and going nowhere.

A. Next February cut the stems of your Lantana back to about 1 1/2 inches from the ground. Fertilize the Lantana with a good quality fertilizer that promotes flowering (rose fertilizer is an example) and water it in lightly. That should take care of the problem.