Forget for a moment Washington’s so-called “swamp” and those who talk of draining it. The city has a big stink, and on Monday, the District government will begin its annual effort to squelch it.

The putrid odor comes from the fruit, or seed pod, of the ginkgo tree — much admired for the brilliant color of its fan-shaped leaves in autumn.

But autumn is also when the female ginkgo drops its fruit on the ground. Burst open or trodden underfoot, the fruit releases an odor that has little parallel in the annals of urban noxiousness.

For years, the District Department of Transportation, which has jurisdiction over street-side trees, has used spraying to curb the ginkgo’s assault on the olfactory senses.

Trees must be sprayed within a narrow window each spring to stop development of the fruit that will foul streets in fall.

As it has for 20 years, the department will spray a chemical called Shield-3EC 24(C), which it described as a mild pesticide.

During the treatment period, weather permitting, the spraying will be conducted over several nights from 9 p.m. through 6 a.m., the department said Friday.

Spraying will start Monday in Ward 5 and go on to Wards 4, 3, 2, 1 and 6, the department said. No female ginkgos are in Wards 7 and 8, according to the department.

Yet, the city acknowledged, not everyone finds spraying satisfactory. It said the treatment does not always work and is sometimes difficult to finish in the time allotted. Some residents also object to pesticide use.

To meet objections, the city said it has a procedure for residents to petition for removal of unwanted ginkgo trees.