by CKR
Pest is defined by the Oxford American Dictionary as "an insect or animal that is destructive to cultivated plants or to stored food etc." I would add weeds to this definition, although, the more I think about it, probably pest is to animal as weed is to plant.
Weeds of the West was useful to me this week. Here's a tumble mustard (Sisymbrium altissimum, not at full powers, will be pulled now that I've taken the photo) and another sort of mustard that I can't find in WoW now, although I was pretty sure I had seen it earlier. Amazing how many weeds are mustards--four-lobed flowers, long skinny seed pods, leaves very variable, related to cabbage and brussels sprouts and broccoli. Even the model for plant genome studies, Arabidopsis thaliana, is a mustard. And it's a weed.
This is a flourishing stand of cheatgrass, the weed I have spent the most time with this week. This bed is somewhat shaded and obviously retains more moisture than some others. The cheatgrass has several different growth habits, and the contrast between the height and greenness of the cheatgrass in this bed and in another 
tells me what kinds of nice plants will do best in these places. I think there is a drip irrigation system, but I don't know where the emitters are. Subject of a more extensive experiment when I get to the place where I can see the soil in the beds...
That second photo shows something else about cheatgrass. It has many different ways it can grow. I've weeded out some so you can see that when the plants are very close together, they raise their seed stalks vertical. But when they are further apart, 
they sprawl.
I can see two things that this adaptability does for cheatgrass: it helps to spread the seeds, launching them on the wind from a thick stand, and dropping them far from an isolated parent; it also allows the cheatgrass to spread its own sort of herbicide to keep other weeds from growing.
Many plants spread chemicals to prevent other plants from growing close to them. Walnut trees are particularly notable, but many trees do it. As a friend said to me, trees hate grass. I suspect that cheatgrass does this for two reasons: it forms almost monocultural stands, and I now see other plants coming up where the cheatgrass was. 
WoW tells me that this is woollyleaf bursage (Ambrosia grayi--Ambrosia, the food of the gods???), a perennial. I was suspecting it to be a perennial because the roots on the plants I've pulled seem to continue down to some infinite bursage source. There wasn't much of it when the cheatgrass was there, but now it's showing up.
Organic gardeners and lovers of furry creatures stop here. You will be offended by what follows.
Because it's a perennial, I'll try dropping some strong Roundup on the centers of the rosettes. More about Roundup and its safe uses in a future Tuesday blog. 
This hole belongs to a rock squirrel (Citellus variegatus), about which nothing good can be said, unless you are an uncritical fan of furry creatures. They carry the fleas that carry plague. They destroy vegetation, including weeds. One area in which they had their burrows was totally devoid of everything, including cheatgrass. The mustards are returning in that area since I got rid of the squirrels, and I plan to improve it still further. However, they find garden plants much more delicious than cheatgrass. I wouldn't mind having them around if they'd eat the cheatgrass. This particular rock squirrel even seems immune to poison, but I think I may be winning. He has also appropriated the space that baby bunny was sheltering in. I haven't seen baby bunny in over a week.
The common feeling is that furry creatures are cuddly and those without fur are yucky. Lauren wrote about this last week. Lauren, I would much prefer those cute little tadpoles eventually growing legs and turning froggy to this squirrel.
I suspect that our preferences in these areas tend to be deep-seated and related to how our ancestors survived. We tamed some of the furry ones who were willing to accept us as alpha pack animals, so they were okay, even friends. And lots of furry ones are edible. Those without fur were frequently poisonous (even some cute froggy ones) and not very edible, so being revolted by them may have been a positive survival trait. Arguably, another survival trait for the race, although not necessarily for the individual, is curiosity. Some of us just had to try to catch anything that moved so that we could look at it better. We found that the non-furry ones aren't necessarily slimy, but rather pleasantly smooth and warm. Even the warty ones are kind of cute.
But this curiosity can work against survival. When I was about four, I had an implement called a "Snippy Scissors," a brightly-painted non-furry electrical scissors. I was fascinated by the buzzing and the way it cut paper without the sharp edges my mother wouldn't let me have. I could see that the and plug had something to do with it, because when it was unplugged it didn't do anything. Maybe it was in those two holes in the wall. I inserted my fingers and luckily got no more than a much stronger buzz than Snippy's. I did instinctively know that it would not be good for my survival to tell my mother about this experiment. And that doesn't come near the time I sniffed hydrogen sulfide, which I'll tell you about sometime later. 
For the race, it's probably a good thing that some individuals have this sort of curiosity. We're the ones who found the new delicious fruits and the best ways to chip rock, not to mention how to use petroleum and how to make (there's that damn squirrel again, out the window!) baby formula. Some of us also died eating the poisonous fruits and taking the quick way across the river. And we figured out how to unleash the power of the atom.
I'll finish with a nice thought. Here's last week's penstemon. There are several others nearby. I think I'll move them to the bed I'm clearing after they bloom.