Q. The leaves of my crepe myrtle are turning yellow some
show signs I think of a specific mold on underside of the leaves. Please advise
in your usual expert advice.
show signs I think of a specific mold on underside of the leaves. Please advise
in your usual expert advice.
A. When yellowing occurs at the tips first it usually
indicates a salt problem. This is possibly due to a lack of water or not enough
water applied during an irrigation. It is also possible water is not delivered
often enough so the soil becomes too dry between waterings. It is also possible
it might be watering too often and not letting the soil dry between waterings.
indicates a salt problem. This is possibly due to a lack of water or not enough
water applied during an irrigation. It is also possible water is not delivered
often enough so the soil becomes too dry between waterings. It is also possible
it might be watering too often and not letting the soil dry between waterings.
.JPG) |
| Crape Myrtle growing at the research center with wood mulch, annual applications of complete fertilizer, iron EDDHA and foliar application of Miracle Gro |
Look closely at your watering habits. If you are watering by
drip make sure you put lots of gallons down every time you water. For trees
this is gallons of water applied each time. The number of gallons depends on
the size of the tree. As the tree gets bigger it needs more water applied at
each irrigation. NOT watered more often.
drip make sure you put lots of gallons down every time you water. For trees
this is gallons of water applied each time. The number of gallons depends on
the size of the tree. As the tree gets bigger it needs more water applied at
each irrigation. NOT watered more often.
Make sure when you water that it is not daily or even
every other day. This time of year every three days is adequate but put enough
gallons down, not a small amount.
every other day. This time of year every three days is adequate but put enough
gallons down, not a small amount.
Estimate how much water is delivered each time you water.
You can use the chart below if you do not know the gph (gallons per hour) of
your drip emitters. For instance if your drip emitter delivers 10 ml of water
in 9 seconds then you have a 1 gph emitter. Increasing the total water applied
will flush salts from the tree.
You can use the chart below if you do not know the gph (gallons per hour) of
your drip emitters. For instance if your drip emitter delivers 10 ml of water
in 9 seconds then you have a 1 gph emitter. Increasing the total water applied
will flush salts from the tree.
Number
of seconds to deliver gph (3600 seconds/hr) (3785ml/gal, approx. 4000)
of seconds to deliver gph (3600 seconds/hr) (3785ml/gal, approx. 4000)
|
Gph
10ml 20 ml 30ml 40ml 50ml 60ml 70ml 80ml 90ml 100ml |
|
¼
36 sec. 72 – – – – – – – – |
|
½
18 36 54 72 |
|
1
9 18 27 36 45 54 63 72 |
|
2
4.5 9 13.5 18 22.5 |
|
3
3 6 9 12 15 |
|
4
2.25 4.5 6.75 9 11 |
|
5
– |
|
6
– |
|
7
– |
|
8
– |
|
9
|
|
10
– – – – 4.5 5.4 6.3 7.6 8.1 9.0 |
If you suspect you are watering too often then increase the
number of emitters (this way you do not need to increase the minutes).
Increasing the minutes means everything else will get more (or too much) water.
number of emitters (this way you do not need to increase the minutes).
Increasing the minutes means everything else will get more (or too much) water.
If you suspect you are not giving enough water each time
then flush the soil with water several times to remove excess salts and rewet
the rootzone deeply. Put a hose at the base of the tree and let the hose run
very slowly around the tree near the emitters for several hours. Or build a
donut around the tree and fill it several times a few days apart. Or buy a
small inexpensive sprinkler that goes on the end of the hose and let it run for
15 to 20 minutes. Repeat every other day three or four times to flush salts.
then flush the soil with water several times to remove excess salts and rewet
the rootzone deeply. Put a hose at the base of the tree and let the hose run
very slowly around the tree near the emitters for several hours. Or build a
donut around the tree and fill it several times a few days apart. Or buy a
small inexpensive sprinkler that goes on the end of the hose and let it run for
15 to 20 minutes. Repeat every other day three or four times to flush salts.
This could also be from a lack of organic matter in the soil
IF the tree is surrounded by rock mulch. Buy some decent compost and apply it
to the rocks under the tree and water it in thoroughly. Do this two or three
times this fall and repeat it in the spring.
IF the tree is surrounded by rock mulch. Buy some decent compost and apply it
to the rocks under the tree and water it in thoroughly. Do this two or three
times this fall and repeat it in the spring.