Xtremehorticulture

Older Agave Yellowing and Not Looking Healthy

Q. My agave is 10 years old and just isn’t looking healthy. I’m afraid of losing it and the surrounding plants. Can’t figure out if it’s too much or too little water. Your expertise would be appreciated. Not a whole lot of information but I am guessing it’s a watering issue. Agaves are usually from the desert Southwest. But it could be agave weevil that damaged the plant earlier in the year. A. Most problems with agaves are from boring into the trunk and roots by the agave weevil and less to do with water. Eventually the immature forms of this insect tunnel into the base and trunk of susceptible plants. Look for them. Agave weevils give birth through their eggs to destructive smaller grubs about 3/8 inch long. They infest the trunk and roots of agave and a few yucca. Look for their damage on older plants later in the year. This is one of the many types of American agaves showing collapse of the leaves due to probably agave weevil. All agaves should have a systemic insecticide applied by spray or soil drench in the spring, no later than March or early April. With spray insecticides it’s important to spray the lower leaves and the surrounding soil at this time. With soil drench insecticides it’s important to apply it to the soil immediately around the plant at the appropriate time. American agave, in particular, is very susceptible to this pest. Be sure the appropriate insecticide is used by reading the label. Example of a liquid garden systemic insecticide that gives at least a couple of months control of insects (picture taken from Amazon)             The agave weevil lays its eggs in susceptible agaves and some yucca when temperatures begin warming in the spring. These eggs are laid by the agave weevil inside the lower leaves, close to the trunk, around that time. A single application of a systemic insecticide is needed around that time. I don’t know of any proven organic methods that control this insect.             If you are still concerned about watering and drainage, make sure that these plants are not watered daily. All perennial plants need the soil to drain away from their roots. Some plants like agave and cacti should never be planted at the bottom of a ridge. Tops are usually okay but not bottoms. Too much water accumulates in those low spots for agave. Other plants may need a continuous moist soils not most agaves and other plants that originate from the desert Southwest.

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Century Plant (American Agave) Not Growing Well

Q. We have a century plant thriving over the past 10-12 years in our front yard. Towards the end of summer, we noticed lower leaves getting soft and tender, leathery even, eventually turning yellow. No new shoots are visible emerging from the core. It gets watered occasionally. Century plant or American agave. A magnet for agave weevils. A. Century plant is an agave weevil magnet! My guess is that’s the problem. The only method I know to control agave weevil is to apply an insecticide around the base of all agaves in March or April of every spring. The insecticide is used to protect the plant from spring infestations. Sprinkle a granular insecticide at the base of the plant and lightly water it. The other option is possibly to drench the soil immediately around the agave with systemic such as imidacloprid (if the label permits).  Warning sign of American agave that it might have agave weevils. Apply granular insecticide in the spring as a prophylactic treatment.             The adult weevils have wings and can fly. They can fly from a neighbor’s plants to a different neighbor’s landscape. These adult beetles lay their eggs in the crotches of the agave in the spring. They don’t use calendars but fly during the spring when it’s perfect weather. That is why the timing for an application is sometime “in the spring”. The “grubs” hatch from the eggs and tunnel inside the core of many different types of agaves and cause their tunneling damage. Sometimes the damage is so severe it kills the plants outright or it might cause a smaller problem when plants are larger. This is the type of problem agave weevil can do on established plants. Notice the base was rotten and the plant “collapsed”.             The other usual problem is watering too often. This can weaken or kill the plant. It doesn’t sound like that is your problem. I would caution you to water the plants deeply and not just a sprinkle them with a hose. Depending on the size of the agave it can take from 5 to 15 gallons of water varying from a small to a large American agave. If the American agave is large, then use three drip emitters located about 12 to 18 inches from the plant in a triangular spacing and watch for signs of stress. Apply water about three to six weeks apart during the summer.

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Joshua Tree Blew Over in the Wind

Joshua tree that blew over Q. I’ve attached a few photos of our Joshua Tree – on the ground! The trunk completely broke during a strong wind on March 25. We planted it 4 years ago and it has grown almost 18″ in that time. Can we replant it in the ground even if it has broken off? Is there any way to save it? Re-grow it? We are heart-broken that it might not be salvageable. A. Unfortunately your Joshua tree is gone. I have never heard of anyone propagating Joshua from above ground stem pieces of the plant.  Base of Joshua tree in the ground             I am curious about why it blew over in the wind. This is not normal for a Joshua tree and makes me wonder if there was another problem associated with the plant. Some people have reported the agave weevil attacking Joshua tree. The agave weevil normally attacks agaves (Joshua is a yucca) with American agave being a favorite of theirs.             This insect is a small snout-nosed beetle that lays its eggs normally at the bases of leaves of the agave. The eggs hatch producing the immature beetle form, a larva or leggless grub. These grubs feed on the stems of agave, normally at the base causing the agave to begin to collapse and rot at the base. Agave weevil in agave crown             If these grubs were present on your yucca (Joshua) it might also cause the base of the tree to rot and collapse as well with the upright part falling on the ground. Visual damage and collapse of yuccas is usually reported in early to midsummer in my experience.             You might look in the remaining stump on the ground and bottom of the blown over portion for 3/8 inch brown to gray snout-nosed beetles or legless off-white grubs of a similar size.

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