Hemp is grown tall and spindly whereas marijuana is shorter and bushier. Also due to cross pollination the hemp will contaminate any marijuana grown close to it, causing the marijuana to loose much of it's THC content and therefore its potency. It would be counterproductive for a marijuana grower, therefore, to grow pot around hemp plants - not that I am any expert on the matter (disclaimer for Agent Mike).
In addition to its obstinate refusal to differentiate between hemp and marijuana, the DEA has also expressed concerns that lawmen would be unable to tell the difference between the two and that people would hide marijuana plants in the middle of hemp fields. That's all bunk, said California cannabis and hemp cultivation expert Chris Conrad.
"First off, this is not a problem for Canadian, British, German, French, and Spanish police, so why are American cops so incompetent compared to the rest of the world, and why should we coddle them for that rather than demand they do their jobs?" he asked. "Also, the fields are registered and police will have the power to enter and inspect at will, so it would be stupid to tell the cops where you're growing, then try to hide marijuana in the field," Conrad pointed out.
The two crops are grown differently for different ends, Conrad noted. "Marijuana is grown for flowering branches, whereas hemp is grown for either stalk or seeds. The stalk crop can be harvested before it flowers, so there would never, ever be any marijuana buds produced." Also, Conrad pointed out, hemp grows straight up and the plants are spaced only a few inches apart, while marijuana plants are shorter and bushier. "Marijuana plants look very different from hemp plants and would be conspicuous from the other plants, especially in an aerial flyover where you would see the area around the marijuana being cleared out from the hemp plants. It's very easy to identify a marijuana patch in a hemp field, and if there is a marijuana plant, it hempifies (is pollinated by the hemp plants) and goes away."
The science and agriculture of hemp probably have little to do with the DEA's intransigent insistence that hemp is marijuana, said Vote Hemp's Eidinger. "This is part of the culture war," he suggested. "When Jack Herer published "The Emperor Has No Clothes" in the early 1980s, the DEA began seeing the call for industrial hemp as part of weakening the links of the criminalization of marijuana." Publication of Herer's book led to a revitalization of interest in industrial hemp, but also associated hemp with the marijuana culture, rather than staid farmers like Hauge and Monson.
http://www.drug-rehabs.org/con.php?cid=4878&state=North%20DakotaOn this page we will explore a myth from Dr. Dave's Industrial Hemp Archives, Hemp and Marijuana: Myths & Realities that law enforcement commonly uses to misdirect the media and legislators.
Myth: Industrial Hemp fields would be used to hide marijuana plants.
Reality: Industrial Hemp is grown quite differently from marijuana. Moreover, it is harvested at a different time than marijuana. Finally, cross-pollination between hemp plants and marijuana plants would significantly reduce the potency of the marijuana plant.
The argument that you can't tell the the different varieties or cultivars of Cannabis apart is a straw man that law enforcement and their lobbyists expect hemp farming supporters to try and knock down. The simple truth is that all you need to tell the difference is GPS coordinates of the farmer's hemp fields and certified oilseed-type or fiber-type varieties grown as you would an agricultural oilseed crop or a fiber crop.
* Industrial hemp is an agricultural crop.
* Industrial hemp is varieties of Cannabis that are low in THC and high in CBD.
* Oilseed and fiber varieties of Cannabis are also known as industrial hemp.
* You can not get drugs from oilseed or fiber varieties of Cannabis.
* Oilseed, fiber, and drug varieties of Cannabis are grown at different densities.
* Drug varieties of Cannabis can not be grown with oilseed or fiber varieties without being easily spotted.
Let's go into more detail.
SNIP
Industrial hemp plants have long and strong stalks, have few branches, have been bred for maximum production of fiber and/or seed, and grow up to 16 feet in height. They are planted in high densities of 100 to 300 plants per square yard. On the other hand, drug varieties of Cannabis are shorter, are not allowed to go to seed, and have been bred to maximize branching and thus leaves and flowers. They are planted much less densely to promote bushiness. The drug and non-drug varieties are harvested at different times, and planting densities would look very different from the air.
Continued here:
http://www.votehemp.com/different_varieties.html