Dan, The Hydro Man (Internet): I have been battling root aphids. I have watered with nematodes twice in two weeks. Now the aphids are walking around on the floor but they are still in the root zone. I set a pyrethrum fogger to take care of the exposed live aphids. I am about to water the soilless planting mix with Botanigard. Then in two days add more nematodes. Do you have any suggestions?
Ed: Most of your efforts are effective. Beneficial nematodes attack most soil dwelling insects. Use pyrethrum as a drench, rather than as a spray or a bomb. This way it gets directly to the insects. Botanigard contains spores of Beauveria bassiana strain GHA. This fungus attacks soft-bodied insects, causing their deaths. It can also be applied as a drench. All three of these treatments can be used concurrently to attack the pests.
Botanigard is available in an organic formulation called sold under the name, Mycotrol A.
The pesticide “Ed Rosenthal’s Zero Tolerance” is an herbal mixture that is often used for root pests. It is also effective.
THE RIGHT TEMPERATURE
Fletch (Internet): My plants are at 31°. Do you think that this is too hot?
Ed: I presume you are taking about the temperature in the plant canopy.
Another, more accurate way to measure temperature is by using a surface temperature thermometer. This provides a reading of the temperature at the leaf surface, rather than of the ambient air.
The correct air temperature is related to the intensity of light and the carbon dioxide content of the air. Plants function in a way similar to cold-blooded animals. Their metabolism and photosynthetic rate increases with increasing temperature. When the temperature is below 15°, no matter how intense the light, virtually no photosynthesis takes place. The photosynthetic rate increases with increasing temperature.
Indoors, a well reflected 600-watt high-pressure sodium (HPS) lamp area provides about 60,000 lumens after loss from light drift and reflective absorption. Placed over a M2 it is considered high intensity. Placed over 1.2 M2 it is considered moderate intensity. Whether under moderate or high intensity light when the temperature can be adjusted, the limiting factor often is CO2. With adequate CO2 levels the photosynthesis rate increases as the temperature rises. The level of CO2 and the ideal temperature is lower for plants under moderate light than plants under higher intensity.
For plants with a moderate intensity light the CO2 level required is about 900 PPM. For plants under high intensity the CO2 PPM level should run about 1300 during the lit period. Cannabis does not use CO2 during the dark period. At these levels the plants thrive at a temperature of 31°.Under moderate light they will probably do better at 26°.
If the plants are being grown in a high ventilation garden that depends on fresh air to replace the CO2, its level is a lot lower. CO2’s ambient level in the atmosphere is only 380 PPM. So even with a high light intensity it cannot photosynthesize as quickly and the temperature for ideal growth is lower. Lower the heat in each situation by about 3°. Too high a temperature results in looser, lankier buds
A thermometer, even in the plant canopy provides an indirect reading of the plant temperature. It measures air temperature. A surface temperature thermometer can provide you with an exact reading of what is happening at the leaf level. Then you can adjust your thermostat accordingly.
CUT LOWER BRANCHES
J. Carlsons (Internet): I have 11 plants growing in a sea of green (SOG) system. They are in the third week of flowering. I noticed the lower side branches are not going to produce much. Is it OK to cut them off so the plant's food and energy can focus more on the bigger top branches?
Ed: Yes, they can be removed. In your SOG system all the action takes place at the top of the canopy. When light hits an opaque surface such as a leaf it gives up almost all of its energy. The only spectrum that passes through is infrared, which is not used in photosynthesis, but is used as a signal by plants to elongate to grow out of the shade. As a result leaves underneath the canopy are in shade and do not produce sugars. Instead they receive energy from the plant, emit moisture and block airflow. For all of these reasons they are a detriment to the plant, which will do better without them.
Marshall Walden (Internet): I am having a problem with snails. I am looking for an organic remedy to protect my garden from them. Is there anything I can use without wasting my precious beer?
Ed: There are a number of things you can do to protect your garden without too much effort. First, remove hiding places that are attractive to them and where they are likely to hang out. They are active at night and on foggy and rainy days. During the day they enjoy a cool moist area such as under boards, and in holes along fences, in debris or tall ground covers. Removing these spaces from the garden makes it far less attractive to them. On the other hand, creating specific moist spaces where they like to congregate can make hand trapping easy. A few boards in the shade or some watermelon rinds make excellent temporary shelters. Once they are apprehended they can be drowned or stepped on and then thrown into the compost left in the garden.
Since they are attracted to moist areas, it is best to water early in the day so the surface has a chance to dry off. Using drip rather than watering large areas limits their territory somewhat.
Beer or a combination of sugar, water and yeast attract the mollusks. To implement the plan dig a little hole and place the container top at soil level. Fill it half way with the beer or sugar-water solution and wait till evening. The creatures will sense the odor and make snail-lines to it, fall in and drown. The snail pub is effective for a radius of about two feet so your garden may require a number of local protective cups.
The two easiest ways to protect the garden from snails is using copper mesh or powdered iron phosphate.
Snails and slugs secrete a slime that helps them move. Researchers think that the copper reacts with the slime electrically and disrupts their nervous systems. Copper flashing, screen or soil can be used around a garden or raised bed perimeter or placed around trays of seedlings or containers with young susceptible plants. If you are placing it around a raised bed or garden perimeter try to eliminate the population from the protected area. The barrier traps any crawlers that are in the enclosed area.
Iron phosphate powder is widely available under two brand names, Slug-Go and Escar-Go. Scatter the powder all around the area you are protecting. When
The mollusks come in contact with it they stop feeding and go to hiding places to die in private. It is pet safe, can be used in organic gardens and is very effective. A single treatment sometimes lasts an entire season and it is economical enough to use to protect large areas.
HERMAPHRODITES FOR FEMINIZED SEED
J.D. (Internet): I am under the impression that to get feminized seeds you cross a hermaphrodite with a female. But I have also heard that about 50% (or so) of those crossed seeds will be hermaphrodite plants and would have to be pulled anyway if an all-female crop was wanted.
Ed: There are several methods of producing feminized seeds, but using hermaphrodites is not a fruitful method. About half the plants will be hermaphrodites and they are harder to detect than males. There are several methods for creating all female seeds. One way is to let buds ripen. Sometimes a few male flowers appear just as the buds ripen. These flowers, which are harmless because the bud is about to be harvested, contain viable pollen that only has female genetics. Be carefully collecting the pollen and using a watercolor brush to pollinate select buds you can produce a small number of seeds.
The second method, and the method used commercially by marijuana seed breeders uses silver containing chemicals silver nitrate and/or silver thiosulfate to chemically alter sexual expression. The resulting male flowers have only female genetics so the resulting seeds produce only female plants. The process is described in more detail in the new edition of Marijuana Grower’s Handbook.
MESSED UP FLOWERING CYCLE
Vince (Internet): The lights in my garden were supposed to be on a 12/12 light cycle for the last 40 days. Yesterday I went into the room and noticed that I had knocked off a segment on the timer so the light was on for 8 hours, off for 15 min and then back on for 3hours 45 minutes. The buds are not growing and the leaves look twisted and weird. The buds have not gotten any larger for 3 weeks. The white hairs are dying on most of the top flowers. If I put them back under the proper light cycle now, will they be OK or should I pull them?
Ed: Plants measure the number of hours of uninterrupted darkness, not the number of hours of light. The small interruption of the light cycle was not long enough to affect the plants’ flowering. All it did was stop photosynthesis because of lack of light. According to your calculations, the plants were getting a total of 12 hours uninterrupted darkness so their flowering should be quite normal. However your description of the leaves and the lack of growth leads me to believe that there were other problems with the light cycle, in which the dark period was interrupted with light early or late in the cycle each day.
I would try to salvage the harvest by making sure the timer is working correctly and the plants are getting 12 hours of uninterrupted darkness each day beginning at the same time. The buds will exhibit a little more growth, and then they ripen up within the next 30 days.