It's hard to identify the culprit without seeing the plant, but my first guess is an infestation of rose slugs. These aren't true slugs, but rather the larvae of the sawfly. The wasp-like adults lay eggs between the leaf layers, and the larvae emerge to feed, leaving translucent "windows" on the leaves. As they grow, the larvae consume entire leaves. Then they drop to the soil to pupate. In some places there may be multiple generations during a summer. Some people report good luck using a neem-based spray as a repellant. If the tiny larvae do emerge and start eating, hose them off with a blast of water daily or handpick and destroy. Natural enemies often keep them in check. If the infestation continues, a spray of neem or insecticidal soap should help. Be sure to spray the entire plant, including the undersides of leaves.
If the buds have holes and are eaten inside, little green caterpillar, called the rose budworm (Pyrrhia umbra), is the likely culprit. Control is difficult because you rarely see the caterpillars. The adults lay eggs on the developing rose buds and, after hatching, the little larvae burrow into the unopened bud to feed. They exit, pupate in the ground, and then emerge as adults. Your best defense is to carefully inspect and remove affected buds, then add mulch over the soil at the base of your rose bush. You can further disrupt the lifecycle by regularly raking the mulch to expose the insects to weather and predatory insects.
Brown beetles are likely rose chafers, which are related to Japanese beetles, and have similar life cycles. Although their preferred foods are rose and peony blossoms, they can also be pests on apple, crabapple, grape, cherry, strawberry, raspberry, hydrangea, hollyhock, and many other ornamental plants and vegetables. There are a number of different controls for rose chafers.
- You can hand pick them: As soon as you see the 1/2-inch-long, light tan, long legged adult beetles, usually the end of June or early July, go out to your rose patch daily to pick the insects off the plants and drown them in a can of water. The adults are only around for a few weeks, so if you are diligent, handpicking works.
- For those without the time or temperament for handpicking, you can spray insecticidal soap. Avoid spraying during the hottest time of the day and don't spray directly on blossoms, as doing so may cause blossoms to deform and can harm pollinators.
- Beneficial nematodes will also reduce the population of rose chafer larvae in the soil without harming earthworms or plants. Spray the nematodes on your lawn in spring or fall (when larvae are in the upper layer of the soil). Timing the spray is important. The nematodes are effective only against the larval stage of the chafer. Spraying when you see the beetles is useless.
Japanese beetles can usually be repelled by using a neem-based spray according to directions. Handpicking is also effective but a bit time-consuming; it works best in early morning or evening when the beetles are moving slowly.
What you're describing sounds like a common problem called mossy rose gall. What you're finding inside are probably not seeds, but eggs or larvae.
Mossy rose galls are caused by Diplolepis spinosa, a cynipid gall wasp. These galls are common on wild roses of North America, from Ontario to Alberta in Canada and throughout most of the northern United States.
The presence of these insects is indicated by the formation of spherical, golf ball-size, spiny galls on the canes of host plants. The galls are unsightly and alter the plant's shape. They also stress the host plant, behaving like nutrient sinks, drawing nutrients away from the rest of the plant. Large numbers of galls on a plant can kill the plant.
Insecticides have no effect on the wasp that causes mossy rose gall. The most effective control is physical removal and disposal of galls in autumn after leaves have dropped and galls are visible. It is important to dispose of all galls since even a single missed gall can produce and reintroduce 30 to 40 mature wasps to the garden the following spring.
It sounds like your rose is suffering from spider mites. These are very tiny and leave a fine webbing on the leaves and stems. To control them, use insecticidal soap according to the label instructions being careful to spray all surfaces of the foliage and stems.
Rose stem borers would do this. They enter newly pruned canes and eat the inside. To try to control them, cut away the canes to healthy wood below. (Make sure you have cut past the borer.) Remove and destroy the trimmings. Cover the ends of the pruned with glue or wax to seal out future borers.
Earwigs are one of those semi-good guys that sometimes become a nuisance (kind of like moles). Although they occasionally chomp on flowers, they also have the habit of chomping on aphids and certain pest larvae. Make sure that what is eating your rose flowers really is earwig -- go out at night with a flashlight to look for them. You can trap earwigs with small boards or moistened newspapers set on the soil around your garden. Pick them up in the morning and dump the earwigs into a can of soapy water. Also, keep your garden free from plant debris and rubbish, where earwigs love to hide.
You may need to use a combination of tactics to control these common pests. Here are a few:
- You can make life hard for them by removing leaf litter or other mulch from the soil surface and spreading a thin layer of sand or crushed egg shells on the ground instead. This will remove their daytime hiding places and create a rough crawling surface which they will avoid.
- Beer traps are shallow containers baited with beer, and can catch a surprising number of slugs! If you begin early in the season, you may be able to control the populations before it gets out of hand.
- Also consider surrounding your most precious beds with copper slug barrier tape. The copper reacts with their “slime” and gives them a shock.
- Try placing boards or hollowed out cantaloupe halves face down in the garden. Each morning, turn them over and gather the pests you find beneath them. This works for slugs, snails, sowbugs, pillbugs, squash bugs, and several other pests.
- Consider planting a variety of flowers and providing a water source to encourage wildlife such as birds and toads to visit your garden. These natural predators can help you in your battle against the slugs.