Uso el pulverizador manual contra el pulgón verde.

Because Spanish often leaves out the subject pronoun when the verb already shows who the subject is.

• uso = I use
• The ending -o tells you the subject is I

So Uso el pulverizador manual... is perfectly natural.
You could say Yo uso el pulverizador manual... if you want extra emphasis, contrast, or clarity, but it is not necessary.

Uso is the present indicative form of usar.

Here it can mean things like:

• I use
• I am using (in some contexts)
• I do use

Most often, the simple present in Spanish covers both a general habit and a present action, depending on context.

Examples:

• Uso este producto cada semana. = I use this product every week.
• Ahora uso el pulverizador manual. = Right now I’m using the hand sprayer.

If you want to strongly emphasize an action happening right now, Spanish can also use:

• Estoy usando el pulverizador manual.

El means the, while un means a/an.

So:

• el pulverizador manual = the manual sprayer
• un pulverizador manual = a manual sprayer

Using el suggests the speaker is referring to a specific sprayer that is already known in the situation or context.

If you were introducing it for the first time, un pulverizador manual could also be possible:

• Uso un pulverizador manual contra el pulgón verde.

That would mean I use a manual sprayer against green aphids/the green aphid.

Pulverizador is something that sprays liquid in a fine mist. In gardening or pest-control contexts, it often means a sprayer.

Manual means manual or hand-operated.

So pulverizador manual means something like:

• manual sprayer
• hand sprayer
• hand-operated sprayer

Depending on the country or context, people might also use other words such as:

• rociador
• atomizador
• fumigador (sometimes, though this can have a slightly different sense)

But pulverizador manual is clear and natural.

In Spanish, adjectives often come after the noun.

So:

• pulverizador manual = manual sprayer
• literally: sprayer manual

This is one of the most common differences from English word order.

Not every adjective always goes after the noun, but for a descriptive adjective like manual, post-noun position is the normal choice.

Contra means against.

In this sentence, it shows that the sprayer is being used to fight, control, or protect against the pest.

So:

• contra el pulgón verde = against the green aphid

This is very natural in Spanish when talking about pests, diseases, and treatments.

Other options may exist in different contexts, but they are not exactly the same:

• para el pulgón verde = for the green aphid
  This can sound less precise if you mean pest control.
• contra clearly communicates opposition or treatment.

Spanish often uses the definite article more than English does.

Here, el pulgón verde can refer to:

• a specific pest being discussed
• the pest as a known type/species
• the general problem in context

Spanish frequently uses el / la / los / las with animals, diseases, pests, and other nouns even when English might use no article or a different structure.

So contra el pulgón verde sounds natural in Spanish.

Yes, it could be plural depending on what you want to say.

• el pulgón verde = the green aphid / green aphid as a pest type / a specific green aphid infestation in context
• los pulgones verdes = the green aphids

Spanish sometimes uses the singular to talk about a species or category in a general way.

If you want to emphasize multiple insects, the plural is also very natural:

• Uso el pulverizador manual contra los pulgones verdes.

So the singular here is not strange; it can sound like referring to the pest in a general or category sense.

Because verde is an adjective that has the same form for masculine singular and feminine singular.

Here:

• pulgón is masculine singular
• so verde stays verde

Examples:

• el pulgón verde = masculine singular
• la planta verde = feminine singular
• los pulgones verdes = masculine plural
• las plantas verdes = feminine plural

So verde only changes in the plural:

• singular: verde
• plural: verdes

The plural is pulgones.

That happens because nouns ending in -ón often lose the written accent in the plural:

• pulgón → pulgones
• camión → camiones

So:

• singular: el pulgón verde
• plural: los pulgones verdes

Pulgón is pronounced roughly like pool-GON, with the stress on the last syllable.

The accent mark on -ón shows that the stress falls there:

• pul-GÓN

Without the accent mark, Spanish stress rules would suggest a different pronunciation, so the accent is necessary.

Yes. That would also be correct, but the meaning shifts slightly.

• Uso el pulverizador manual...
  This can mean I use the manual sprayer in general, or simply state the action.
• Estoy usando el pulverizador manual...
  This emphasizes that the action is happening right now.

So both are possible, but uso is more neutral and broader.

The normal, neutral order is:

• Uso el pulverizador manual contra el pulgón verde.

Spanish word order is somewhat flexible, but changing it usually adds emphasis or sounds more marked.

For example:

• Contra el pulgón verde uso el pulverizador manual.

This is understandable, but it feels more emphatic or stylistic. For a learner, the original order is the safest and most natural choice.